If I try to change the Meta Title and Meta Description for Categories and I save it... the save doesn't seem to apply. I have tried several times and refreshed page several times. Deleted cookies etc and Meta title and meta description are not updated for Categories. I am using Osclass 3.9, Gamma theme and All in One SEO version 3.1.2

@bobyrou
Have you tried to reinstall plugin? If some data are not stored, it usually means database table is missing. You may also check on database if all tables from struct.sql are created.
If yes, create support ticket.