I have been occasionally getting this error message for a while (across multiple Unity versions):
Internal: JobTempAlloc has allocations that are more than 4 frames old - this is not allowed and likely a leak
Since I upgraded to Unity 2018.2, this error message is followed by this one:
To Debug, enable the define: TLA_DEBUG_STACK_LEAK in ThreadsafeLinearAllocator.cpp. This will output the callstacks of the leaked allocations
However, I don't have access to ThreadsafeLinearAllocator.cpp. It would be helpful if debugging for leaked allocations could be turned on, or at least if we had the option to.