We still have no idea why RenderType.getEntityTranslucent() is broken. It seems to not like rendering water behind it and sometimes entities behind it are invisible. If anyone wants to take a look at this it would be greatly appreciated!

ok

Have you tried changing the 'translucency' to something else one line before the original bug?
RenderType.getEntitySomething else()
RenderType.getEntityTranslucent()

This fix usually works in python, i don't usually do java.

This is a bug with the vanilla rendering engine, and was fixed in 1.16 when they introduced a proper depth buffer. This will not be a one-line fix and will probably require a whole bunch of mixins/coremodding.