Hi, I already opened an issue for this problem, but I didn't upload the right crash log.
Here it is
Same problem here : Server crashes when entering the Lost Cities Dimension.

Hmm weird. I cannot reproduce that. Maybe some other mod is breaking things?

i think it's beacause of the BYG mod. Can we configure Lost Cities to use the vanilla world generator ?

Lost cities can't do that. That's for byg

ok thanks, I'll ask to the modder.I'll keep you informed asap

No news from the modder. I still have this problem but the Lost Cities seems to generate normally in the overworld. So I will remove the possibility to join the dimension.
Sorry for the inconvenience and good luck with the development!