Operating system: Linux-5.4.0-42-generic-x86_64-with-debian-bullseye-sid 64 Bits
Graphics card: Quadro GP100/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 440.100
Broken: version: 2.90.0 Beta, branch: master, commit date: 2020-08-02 18:54, hash: rB0264f53e30c7
Short description of error
When using the multires modifier for sculpting the performance seems to suffer significantly for certain brushes. This gets even worse on lower levels so the performance often is much worse on level 1 when compared to level 3.
The performance seems to be especially bad on the Clay & Clay Strips brushes.
Example .blend file
Just to make sure the performance is as reproducible as possible, here is the file of the jacket.
When trying to reproduce this performance on a cube or Suzanne head it wasn't as bad but still noticeable.