Operating system: Darwin-19.4.0-x86_64-i386-64bit 64 Bits
Graphics card: AMD Radeon Pro 5500M OpenGL Engine ATI Technologies Inc. 4.1 ATI-3.8.24
Broken: version: 2.83 (sub 11), branch: master, commit date: 2020-03-26 23:49, hash: rBf1fb3eb97540
Short description of error
When using a cloth physics simulation, if you add or remove a material from an object, the cloth system cache is reset ("cache is outdated"). I don't think the material affects the cloth physics in any way (as it seems you can change any parameter within the material without the cache resetting), and therefore this should probably not happen. Please correct me if I am wrong and the material does affect the physics somehow.
Exact steps for others to reproduce the error
In the default scene, enable cloth physics for the cube. Let the playback run for a few frames, building up the cache. Add a material to the cube; now the cache gets reset.