Operating system: Linux-5.3.0-26-generic-x86_64-with-debian-buster-sid 64 Bits (Ubuntu 19.04 and 19.10)
Graphics card: GeForce RTX 2080/PCIe/SSE2 NVIDIA Corporation 4.5.0 NVIDIA 435.21
Broken: version: 2.81 (sub 16), branch: master, commit date: 2019-12-04 11:32, hash: rBf1aa4d18d49d
Short description of error
Rigged character is linked to a scene, then Object/Relations/Make Proxy is used to make proxy armature. When the character is animated using the proxy armature, the animation looks fine when run in the viewport, but when rendered (either in Cycles or Eevee), there are random glitches in single frames (different each time you render) where the character is suddenly in another position -- often far away from where it should be and strangely twisted.
I have to work around the problem by rendering the faulty frames again as separate png files -- which works because the glitch hits different frames each time you render.
If I open the same file in 2.80 it works fine. If the animation is already in the linked object and no proxy armature is used, it works fine.
Exact steps for others to reproduce the error
Sorry, but this issue is very random and I have not been able to produce a test file to reproduce it. It is possible that it only happens when there are several rigged/animated objects in the scene, but I am not sure.