profile:
profile_rarecities.txt

crash log:
crash-2019-03-21_19.42.19-server.txt

I'm very very inexperienced with java, all I can tell is that it seems to be something in lost cities itself and not a mod incompatibility. The only thing I've done to this profile from the default is restrict the biome generation to the biomes listed in the profile, increased the max building height, and increased minimum building basements to 1. It seems to happen randomly. I've flown around and generated plenty of chunks, and I thought I had the problem solved, until eventually someone flew into a chunk that errored and took down the server. I have no idea what the chunks that cause problems have in common.

A maximum of 25 floors is extremely high. There are 6 levels per floor so that's 150 levels for a maximum sized building. If that's placed on a high hill you can get issues. I'm guessing that could be (part of) the problem