Not sure if this is Terrestria's fault or something quirky and unavoidable. That's a Caldera beach transitioning to a beach, then a river, then a lukewarm ocean, then an ocean over a distance of about 20 blocks. The upper water is all in the Caldera Beach biome.

To be clear, I'm running the Overworld Two mod, which is supposed to do generally the same thing as vanilla but will produce different results than vanilla given the same seed.

Other potentially relevant mods for reproducing this include traverse, terrestria, cinderscape, and wild explorer with pumpkin pastures and cherry oak forests disabled.

Hmm, can you try to replicate the issue without overworld-two? Sometimes mod conflicts can cause caldera biomes to get cut off like that

Currently I cannot replicate the issue with or without overworld-two >_>

Just wanted to say I have seen this a few times too, (with overworld two). We can't replicate this issue without OW2 because there is no seed parity with vanilla.

This is not a problem with overworld-two as overworld-two doesn't change biome generation