We have been deploying Windows 10 1607 across a number of networks along with avast.
We have found that the combination of Avast, Lenovo Devices with a SSD and Windows 10 1607 cause issues with operating system functionality mainly the Windows 10 start menu.
When we remove avast, the issues disappear and the operating system works correctly.
We have turned on Windows defender as and interim solution until this can be fixed.
And remove the client completely using the tool. Then do a clean install. If the issue persists, get the Avast logs (you can zip then attach here), for most systems they are here: C:\ProgramData\AVAST Software\Avast\log
We can see if there is anything showing in the logs.
Too, post the model of computer and model of SSD showing in Device Manager, as it may be helpful to any of the avast team that is watching.
Too, I would advise opening a support case at support.avast.com, mention this forum posting in your ticket so they can see you are not alone in the issue.