Lisle, you're welcome. I hope the problem is solved now. I saw more problems like these (collation errors) in the forums.
The problem in our database was caused by a different collation (utf8_general_ci) that was imported from a database dump from another migration. After upgrading from 3.5.4+ to 3.5.5+ this collation error occured for the first time.
Installing and upgrading help
Error reading database - solved. BUT WHY???
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