The issue was that the same point cache was read by multiple threads at the same time (the same object was evaluated for render and for the viewport). Both threads incremented PTCacheMem->cur which lead to the crash. The fix is to remove the PTCacheMem->cur and store it on the stack instead. This way every thread has its own cur. Reviewers: brecht Differential Revision: https://developer.blender.org/D9606