A lot of users faced inaccessible Outlook Web Access after CU6 installation. This can also affect users who reissue “Microsoft Exchange Server Auth Certificate” (if they are running CU6 version).
This is applied to situation when user gets “Something went wrong” and error with ID 500, on the server side warning appeared in the eventLog as:
Log Name: Application
Source: ASP.NET 4.0.30319.0
Date: 3/24/2018 12:46:43 PM
Event ID: 1309
Task Category: Web Event
Event code: 3005
Event message: An unhandled exception has occurred.
Event time: 3/24/2018 12:46:43 PM
Event time (UTC): 3/24/2018 8:46:43 AM
You should get following phrase in the logEntry: Encryption certificate is absent
This is Microsoft guys, you will never understand whats going wrong when you read log error.
As a workaround you can change your TimeZone to match UTC. From my event you can see that the time is 12:46 PM, just change time zone to UTC, in my case time has been changed from 12 PM to 8 AM and issue with OWA disappeared. I suppose that you can roll-back your timeZone (in my example with GMT +4 timeshift to UTC is 6 hours).
So thanks to Microsoft that they are pushing us out to use O365:)
Update: After 6 hours I changed time zone back and did IISRESET, everything is working so far.