Reproduction steps:
1. Open project attached (ClothAnimationCrash.zip).
2. Enter play mode.
3. Enable Skinned Mesh Renderer (Plane->PlaneAnimation&Clot->Plane04->Skinned Mesh Renderer).

Expected result: Skinned Mesh Renderer will be shown, the console will stay clean.
Actual result: Error "Assertion failed" appears with a warning "JobTempAlloc has allocations that are more than 4 frames old.."
Full error message: Assertion failed: Assertion failed on expression: 'Thread::EqualsCurrentThreadIDForAssert(Thread::mainThreadId)'

Notes: After about 30 seconds, objects fall from the sphere and another "bunch" of errors are spammed in the console. Before entering play mode, make sure to have object "PlaneAnimation&Cloth" or its Skinned Mesh Renderer disabled.

Reproduced on: 2018.1.0a1.
Works fine on: 5.5.4p4.
Could not test on other versions due to another issue.