when trading with a cartographer and they level up from a novice up, you freeze get disconnected and then get a server watchdog crash as your player is still connected but not able to do anything / able to reconnect. it seems to be when its creating a map trade idk.
for version:
numismatic-overhaul-0.2.8+1.19.jar.

File attached is a log for the crash (may be missing a bit as i had to copy it from the terminal rather than the file)
crashlog.txt

This issue is related to vanilla, and happens due to the server lagging out while the cartographer is searching for a specific structure. It is not something we can exactly fix within Numismatic Overhaul.

I do recommend a mod like Structure Essentials, as it heavily improves this search algorithm, possibly preventing your server from lagging out.
https://www.curseforge.com/minecraft/mc-mods/structure-essentials-forge-fabric

Alternatively, in your servers server.properties file (server config), you can increase the max-tick-time to something higher. I believe 120000 ticks (2 minutes) is usually required for slow servers + heavy modpacks.