I created a bugreport T80859 earlier.
The problem is in the file source/blender/editors/sculpt_paint/paint_image_proj.c (line numbers against commit d376aea61)
at the lines 5309 and 5320 the functions IMB_rect_from_float(...) and IMB_float_from_rect(...) are called from threaded code on a shared ibuf.
However, ps->reproject_ibuf is shared between threads, so this is not thread-safe.
This is a race condition and leads to wrong output when projecting float data onto a uchar texture or vice versa on a multithreaded system.
The checks on line 5308 and 5319 are already a race condition.
I created this patch which fixes the problem , but I'm not sure if I'm overlooking something.
This makes sure reproject_ibuf contains the correct formats *before* the threadpool is started.
I replaced the original location of the conversions with BLI_asserts(). That may be overkill?