The answer in this post explains what setting you need to adjust: https://forum.mendix.com/link/questions/86069
I might not be an expert at this, but from what I see is that, users who logs in, are not correctly loging out. So the sessions reserved for users who have logged in is not getting freed. And this reduces the amount of free sessions for the users who newly logs in.
Try creating a timeout, and force a logout after a certain time of inactivity.
Hope this helps
You might also find this document helpful. These are settings that could be added to the service console to free up connections when not being used.