3rd post at least mentioning spikes.
Like for the others:
Either the engine is bugged (test it with a valid heightmap that actively works in prior engine versions)
Or your heightmap files are invalid.
Only 16bit files. Usually PNGs.
Ps:
The first image just makes it look like your files are bad btw. It’s got some shape to it, so perhaps you ended up with corrupt files by manaully editing them in photoshop or some other non compatible with 16bit program…