I am having a simultaneous session limit reached on so many users on hotspot login.

Below is one users log
17:16:31 hotspot,info,debug kar309 (10.10.3.89): trying to log in by http-chap
17:16:33 hotspot,info,debug kar309 (10.10.3.89): login failed: simultaneous session limit reached

I would like to know what may be going on?

user is in login ..
check time out or test remove old user and rebilld the user manager database

You probably reached Your license limit on number of hotspot active users.
Check this link:

https://wiki.mikrotik.com/wiki/Manual:L ... nse_Levels