It is exactly as it appears. I have messed with the compatibility settings, fiddled with the cutoff distances and LODs, disabled both Intel and AMD graphics fixes (I use Nvidia), and tried enabling both, none, and one of each of the render modes.

This is expected.
A rough generator will have to be written for Terra++ terrain and that will have to wait until Terra++ 2.0 is out with support for multi-resolution datasets.

There is not ETA, no one is working on Terra++ right now.

I observed this issue on the version currently hosted on CurseForge, but not on Build 728. True to your word, it does load extremely slowly on this build and does work as intended.

while what SmylerMC said is technically correct, fp2 should still be able to load in terrain without a terra++ rough generator (albiet much slower). if you look closely at the screenshot, you can tell that it actually is:

this little bump of terrain has to be being rendered by fp2 - vanilla doesn't render terrain in that shape.

that said, the area being rendered by fp2 should have been expanding at a visible rate. was it not? if not, that's a bug.