Caves occasionally generate with these blocky areas.
These areas generate pretty much everywhere and multiple were found while flying around in spectator mode. No specific world type is required to recreate this issue, just the default world settings.
The seed I used: -1695745861
One of these blocky areas can be found at the coordinates in the screenshot.
A few other things I would like to note:
- This world was created on 21w10a, so there shouldn't be any chunk misalignments caused by conflicting generation.
- This issue is similar to MC-218729, however this doesn't just happen at aquifers. In fact, I have found some that generate nowhere near water.