Hi, I think so I found a bug in Raspberry Pi Mystic ver. 1.12 a46.
In Configuration, Login/Matrix MENU:

Login Attemps = 1 .......... No new users are allowed.
This value must be 2 or more.

telnet sotanomsxbbs.org:23
*The last Msx user in Ibiza*

--- Mystic BBS v1.12 A46 2020/08/26 (Raspberry Pi/32)
* Origin: Sotano Msx BBS (21:1/150)