That could be it - it is very random and it is hard to debug - but all I know it is something to do with coroutines if I remember.
Going through old messages it was this:
Assertion failed: Assertion failed on expression: 'coroutine->m_RefCount > 0'
Assertion failed: Assertion failed on expression: 'coroutine->m_CoroutineEnumeratorGCHandle.HasTarget()'