Running an application that uses MPI, OpenMP tasks in MPI_THREAD_MULTIPLE mode I get this error;
 trying to free memory block that is currently involved to uncompleted data transfer operation
free mem - addr=0x7fffc40812d0 len=175104
RTC entry - addr=0x7fffc4081300 len=175056 cnt=1
Assertion failed in file ../../i_rtc_cache.c at line 1408: 0
This has been compiled with Intel 17 and uses Intel MPI 17.
The error message is indicative of a possible programming error on your part were an allocatable data object/array/vector/container has been use in a source for an MPI message to another rank and where the object is destroyed prior to the completion of the transmission.
One case that bit me was with using OpenMP tasking and forgetting to have a correctly placed taskwait.