tetra's structures only spawn in cold biomes and even then this crash is not guranteed making it not entirely consistent to reproduce, but it does seem to happen and i managed to do it in a clean instance with:

subwild: 1.16.3-1.0
tetra: 1.16.3-3.1.0
mgui: 1.16.3-3.1.2

crash report

I am having this same issue. My crash reports mention "tetra:feature" and SubWild's spleleotherms. The thread about eidolon might be discussing an issue with the same cause.