XML layout issue after update to 2.2.1 (from 2.1.10)

[olukyanenko]

After update to 2.2.1 I get next error:

main.INFO: Cache file with merged layout: LAYOUT_adminhtml_STORE2_391fccd54da687afc76a5d6559b714906 and handles default, adminhtml_dashboard_index: Please correct the XML data
 and try again. Element 'css': This element is not expected.
Line: 4

Did magento 2.2 change layout XML syntax?

How to debug this issue? How to find out which file has wrong syntax?

[Damian Culotta]

Hi @olukyanenko,

I'm not completely sure but I've tracked some similiar issues to https://magento.stackexchange.com/questions/199151/magento-2-2-0-upgrade-error-attribute-type-is-not...

Can you check if this is useful?