I read numerous reports like this and one of two things usually fix the issue.
Wipe the cache partition (won't loose any personal apps or data) from Android System Recovery or do an FDR (Factory Data Reset). Be sure to back up your data before you do an FDR. Although Marshmallow is supposed to back up app data, I still prefer to do my own backup, just in case.
Obviously, try wiping the cache partition and see if that works first.
Just one of the reasons I don't do OTA's anymore. If I have to an FDR to fix what breaks after waiting forever for the OTA, then I might as well flash the complete image myself the day Google releases the image.