Magento 2.3.1 upgrade errors/issues

[mmdigital]

Just upgraded to Magento 2.3.1 and when in developer mode front end does not load properly and I get these errors, but in production mode page does load properly. I've had to disable several extensions due to incompatibility or lack of updates for new version. Need help finding out what is causing these issues in development mode and how I can fix them. thanks

1 exception(s):
Exception #0 (Magento\Framework\Config\Dom\ValidationException): Element 'referenceContainer', attribute 'as': The attribute 'as' is not allowed.
Line: 24

Element 'referenceContainer', attribute 'before': The attribute 'before' is not allowed.
Line: 24


Exception #0 (Magento\Framework\Config\Dom\ValidationException): Element 'referenceContainer', attribute 'as': The attribute 'as' is not allowed.
Line: 24

Element 'referenceContainer', attribute 'before': The attribute 'before' is not allowed.
Line: 24

<pre>#1 Magento\Framework\Config\Dom->__construct('<layout xmlns:xs...', &Magento\Framework\App\Arguments\ValidationState#000000001097f53f000000003736c318#, array(), NULL, '/home/283760.clo...', '%message%\nLine: ...') called at [vendor/magento/framework/ObjectManager/Factory/AbstractFactory.php:116]
#2 Magento\Framework\ObjectManager\Factory\AbstractFactory->createObject('Magento\Framewor...', array('<layout xmlns:xs...', &Magento\Framework\App\Arguments\ValidationState#000000001097f53f000000003736c318#, array(), NULL, '/home/283760.clo...', '%message%\nLine: ...')) called at [vendor/magento/framework/ObjectManager/Factory/Dynamic/Developer.php:66]
#3 Magento\Framework\ObjectManager\Factory\Dynamic\Developer->create('Magento\Framewor...', array('xml' => '<layout xmlns:xs...', 'schemaFile' => '/home/283760.clo...', 'validationState' => &Magento\Framework\App\Arguments\ValidationState#000000001097f53f000000003736c318#)) called at [vendor/magento/framework/ObjectManager/ObjectManager.php:56]
#4 Magento\Framework\ObjectManager\ObjectManager->create('Magento\Framewor...', array('xml' => '<layout xmlns:xs...', 'schemaFile' => '/home/283760.clo...', 'validationState' => &Magento\Framework\App\Arguments\ValidationState#000000001097f53f000000003736c318#)) called at [vendor/magento/framework/Config/DomFactory.php:43]
#5 Magento\Framework\Config\DomFactory->createDom(array('xml' => '<layout xmlns:xs...', 'schemaFile' => '/home/283760.clo...', 'validationState' => &Magento\Framework\App\Arguments\ValidationState#000000001097f53f000000003736c318#)) called at [vendor/magento/framework/View/Model/Layout/Update/Validator.php:141]
#6 Magento\Framework\View\Model\Layout\Update\Validator->isValid('<layout xmlns:xs...', 'layout_merged', false) called at [vendor/magento/framework/View/Model/Layout/Merge.php:476]
#7 Magento\Framework\View\Model\Layout\Merge->_validateMergedLayout('LAYOUT_frontend_...', '<container name=...') called at [vendor/magento/framework/View/Model/Layout/Merge.php:457]
#8 Magento\Framework\View\Model\Layout\Merge->load(array('1column')) called at [generated/code/Magento/Framework/View/Model/Layout/Merge/Interceptor.php:193]
#9 Magento\Framework\View\Model\Layout\Merge\Interceptor->load('1column') called at [vendor/magento/framework/View/Page/Layout/Reader.php:93]
#10 Magento\Framework\View\Page\Layout\Reader->read(&Magento\Framework\View\Layout\Reader\Context#000000001097f09b000000003736c318#, '1column') called at [vendor/magento/framework/View/Page/Builder.php:67]
#11 Magento\Framework\View\Page\Builder->readPageLayout() called at [vendor/magento/framework/View/Page/Builder.php:54]
#12 Magento\Framework\View\Page\Builder->generateLayoutBlocks() called at [vendor/magento/framework/View/Layout/Builder.php:65]
#13 Magento\Framework\View\Layout\Builder->build() called at [vendor/magento/framework/View/Layout.php:253]
#14 Magento\Framework\View\Layout->build() called at [vendor/magento/framework/View/Layout.php:875]
#15 Magento\Framework\View\Layout->getBlock('page_content_hea...') called at [generated/code/Magento/Framework/View/Layout/Interceptor.php:414]
#16 Magento\Framework\View\Layout\Interceptor->getBlock('page_content_hea...') called at [vendor/magento/module-cms/Helper/Page.php:171]
#17 Magento\Cms\Helper\Page->prepareResultPage(&Magento\Cms\Controller\Index\Index\Interceptor#000000001097f662000000003736c318#, 'home') called at [vendor/magento/module-cms/Controller/Index/Index.php:74]
#18 Magento\Cms\Controller\Index\Index->execute(NULL) called at [generated/code/Magento/Cms/Controller/Index/Index/Interceptor.php:24]
#19 Magento\Cms\Controller\Index\Index\Interceptor->execute() called at [vendor/magento/framework/App/Action/Action.php:108]
#20 Magento\Framework\App\Action\Action->dispatch(&Magento\Framework\App\Request\Http#000000001097f418000000003736c318#) called at [vendor/magento/framework/Interception/Interceptor.php:58]
#21 Magento\Cms\Controller\Index\Index\Interceptor->___callParent('dispatch', array(&Magento\Framework\App\Request\Http#000000001097f418000000003736c318#)) called at [vendor/magento/framework/Interception/Interceptor.php:138]
#22 Magento\Cms\Controller\Index\Index\Interceptor->Magento\Framework\Interception\{closure}(&Magento\Framework\App\Request\Http#000000001097f418000000003736c318#) called at [vendor/magento/framework/Interception/Interceptor.php:153]
#23 Magento\Cms\Controller\Index\Index\Interceptor->___callPlugins('dispatch', array(&Magento\Framework\App\Request\Http#000000001097f418000000003736c318#), array(array('designLoader', 'customerNotifica...', 'catalog_app_acti...', 'tax-app-action-d...', 'weee-app-action-...', 'storeCheck', 'contextPlugin', 'customer-app-act...'))) called at [generated/code/Magento/Cms/Controller/Index/Index/Interceptor.php:39]
#24 Magento\Cms\Controller\Index\Index\Interceptor->dispatch(&Magento\Framework\App\Request\Http#000000001097f418000000003736c318#) called at [vendor/magento/framework/App/FrontController.php:159]
#25 Magento\Framework\App\FrontController->processRequest(&Magento\Framework\App\Request\Http#000000001097f418000000003736c318#, &Magento\Cms\Controller\Index\Index\Interceptor#000000001097f662000000003736c318#) called at [vendor/magento/framework/App/FrontController.php:99]
#26 Magento\Framework\App\FrontController->dispatch(&Magento\Framework\App\Request\Http#000000001097f418000000003736c318#) called at [vendor/magento/framework/Interception/Interceptor.php:58]
#27 Magento\Framework\App\FrontController\Interceptor->___callParent('dispatch', array(&Magento\Framework\App\Request\Http#000000001097f418000000003736c318#)) called at [vendor/magento/framework/Interception/Interceptor.php:138]
#28 Magento\Framework\App\FrontController\Interceptor->Magento\Framework\Interception\{closure}(&Magento\Framework\App\Request\Http#000000001097f418000000003736c318#) called at [vendor/magento/module-store/App/FrontController/Plugin/RequestPreprocessor.php:94]
#29 Magento\Store\App\FrontController\Plugin\RequestPreprocessor->aroundDispatch(&Magento\Framework\App\FrontController\Interceptor#000000001097f582000000003736c318#, &Closure#000000001097f5e2000000003736c318#, &Magento\Framework\App\Request\Http#000000001097f418000000003736c318#) called at [vendor/magento/framework/Interception/Interceptor.php:135]
#30 Magento\Framework\App\FrontController\Interceptor->Magento\Framework\Interception\{closure}(&Magento\Framework\App\Request\Http#000000001097f418000000003736c318#) called at [vendor/magento/module-page-cache/Model/App/FrontController/BuiltinPlugin.php:73]
#31 Magento\PageCache\Model\App\FrontController\BuiltinPlugin->aroundDispatch(&Magento\Framework\App\FrontController\Interceptor#000000001097f582000000003736c318#, &Closure#000000001097f5e2000000003736c318#, &Magento\Framework\App\Request\Http#000000001097f418000000003736c318#) called at [vendor/magento/framework/Interception/Interceptor.php:135]
#32 Magento\Framework\App\FrontController\Interceptor->Magento\Framework\Interception\{closure}(&Magento\Framework\App\Request\Http#000000001097f418000000003736c318#) called at [vendor/magento/framework/Interception/Interceptor.php:153]
#33 Magento\Framework\App\FrontController\Interceptor->___callPlugins('dispatch', array(&Magento\Framework\App\Request\Http#000000001097f418000000003736c318#), NULL) called at [generated/code/Magento/Framework/App/FrontController/Interceptor.php:26]
#34 Magento\Framework\App\FrontController\Interceptor->dispatch(&Magento\Framework\App\Request\Http#000000001097f418000000003736c318#) called at [vendor/magento/framework/App/Http.php:136]
#35 Magento\Framework\App\Http->launch() called at [generated/code/Magento/Framework/App/Http/Interceptor.php:24]
#36 Magento\Framework\App\Http\Interceptor->launch() called at [vendor/magento/framework/App/Bootstrap.php:258]
#37 Magento\Framework\App\Bootstrap->run(&Magento\Framework\App\Http\Interceptor#000000001097f45a000000003736c318#) called at [index.php:39]
</pre>

[jamescowie]

I've had this problem before. Simple put one of your XML layout files using a structure that is no longer valid. If you are using phpstorm and have the xsd configured to validate document it should flag nicely which is not validating because of this error. Just look for one that is using ”as” I'm its node and update. 

It sounds like you disabled all external modules to debug this and the problem existed so it should make hunting down in your custom work a little easier. 

[Sunil Patel]

Hello @mmdigital 

your theme and module is not compatible with the latest Magento.

if you are using any purchase theme or module then upgrade it.

If you have did custom development then check @jamescowie  reply.

Hope it will help you, if works then mark as a solution.