@Arnel ... one can run any OS on the hardware you have. Do you run Linux or Windows?
Don't do Windows any more and can't help.
If linux, what OS (Ubuntu/CentOS and version?
Will say this that value for max_allowed_connections sounds like a lot for 600+ users - are those 600+ users connected at one time?
If one has that much traffic it might be that you need to have a dedicated machine for DB.
Individual workstation/users access issues almost have to do that one by one ... each might be different.
References in error logs?
'spirit of sharing', Ken