System Information
Operating system: Windows-10-10.0.19041-SP0 64 Bits
Graphics card: GeForce GTX 1080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 456.38

Blender Version
Broken: version: 2.90.0, branch: master, commit date: 2020-08-31 11:26, hash: rB0330d1af29c0
Worked: (newest version of Blender that worked as expected)

Short description of error
I was just painting, testing out all the different PBR map types, and suddenly the bump map started rendering with heavy banding, like the resolution dropped.
I tried different size bump map texture sizes and it happens with all. Included file has a 4k bump map, and you can still see it happening, but only in the 3D view.

A second problem is that I can't paint on the model if I zoom in pretty close, and the distance changed while testing. At one point I couldn't get it closer than a foot from the screen, but other times I could get much closer, but still I reach a point where it doesn't paint anymore and I'm not clipping into it.

Exact steps for others to reproduce the error
I can't reproduce the banding exactly, not sure what's causing it but maybe you can find the problem in the included file. I got it to happen in another file by just scribbling and smudging on the bump map randomly, but it didn't get as bad as this one. I notice that the 3D view generally has a lower, more pixelated display of the bump map than it should.