I have the same issue. With Windows, it seemed to start working when I reached about 30 users. Once I switched over to Linux, I'm having the problem again, and I'm in the 70s for users now.
Just a note:
Some of the data files are linked. If you separate mystic.dat and users.dat
in any way, you are going to get users with bad indexes. For example if you copy over mystic.dat and then copy over users.dat at another time, or vice versa, you'll get this.
They have to never be "separated" from each other. Restoring a mystic.dat
from backup means you have to also restore the users that went along with it.
Usually people do some sort of backup restore when this issue pops up.
I really need to unlink those two datafiles. I've been meaning to for a long time now.
--- Mystic BBS v1.12 A35 (Windows/32)
* Origin: Sector 7 [Mystic BBS WHQ] (21:1/108)