After update Magento 2.0.0 to 2.0.2 successfully by using composer, I can not get any error message or success message.
Example: I login with wrong login information, the error message "Invalid login or password." does not appear.
When I turn version 2.0.2 to 2.0.0, the messageManager is working again.
But I install 2.0.2 directly, the messageManager works correctly
I find the issue, there is some error on My Theme's style.less and It has not been compiled successfully.
It maybe cause that Magento_Theme has not been compiled successfully.