Hrmm, I wasn't able to reproduce after some corrections. Means I probably reproduce it incorrectly.
In that case - Are you doing it alone, or as a group on the non GM chars?
I had been encountering it reliably with both solo and as a group when non-GM characters are present in V15. I have so far only tested as a group in V16, however I am happy to test solo again as well if it would help. The group consisted of two actual players, no bots.
This is the message the server gave me when the crash happened:
C:\Users\Emil\Desktop\Emulation\EC2021\EC2020newGOLD\EC434_2022\src\server\game\Entities\Object\Object.h:962 in WorldObject::GetMap ASSERTION FAILED: