Usernames case sensitive after upgrade

[cirdok2]

We have upgraded from 3.8 to latest 5 and logins are now case sensitive. This is a test upgrade to become more familiar with 5, but we cannot go live this way since will cause many problems to our current users.
Any idea what could have caused this to happen or what to check?
Thanks!

[cirdok2]

Solved

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Make sure character set is not defined in field definition i.e. "character set utf8 collate utf8_bin" or similar.