Hi Zeno410 (And TimBurton).
Okay, I've found a reproducible case. Took me a while to binary chop down to something more manageable and find the mods that seem to make a difference.
Mods I used:
Enchiridion 2 2.0.2a
JourneyMap 5.1.3 unlimited
Mariculture Deluxe 18.104.22.168a
Create realistic world with seed: 1829934433
/tp 1883 100 -1121
There's a transition here with between Desert and Praire that shows the problem.
If I disable Mariculture and dependency Enchiridion 2 the problem seems to go away.
TimBurton had Mariculture in his list too.
Hope that helps somehow, of course the simple solution is to not use Mariculture.