Hi Junchao, We do not have any plans to provide another MPICH release in the 3.3.x series. It is good to know this bug is fixed in the latest version of MPICH. Ken On 3/2/21, 8:17 PM, "Junchao Zhang via discuss" <[email protected]> wrote: Hello, We met an error with mpich-3.3.2 and ucx-1.8.0. See the attached example, which uses a user defined data type in MPI_Startall. MPICH was configured with --with-device=ch4:ucx --with-ucx=/path/to/ucx-1.8.0. The error stack is $ mpirun -n 2 ./dtype Assertion failed in file src/mpi/datatype/type_free.c at line 38: (((datatype_ptr)))->ref_count >= 0 /home/jczhang/soft/lib/libmpi.so.12(+0x48fa1f) [0x7f4019b6ba1f] /home/jczhang/soft/lib/libmpi.so.12(MPL_backtrace_show+0x18) [0x7f4019b6baff] /home/jczhang/soft/lib/libmpi.so.12(+0x441e27) [0x7f4019b1de27] /home/jczhang/soft/lib/libmpi.so.12(+0xfebc2) [0x7f40197dabc2] /home/jczhang/soft/lib/libmpi.so.12(MPI_Type_free+0x5fd) [0x7f40197db239] It does not happen with mpich-3.4.1. --Junchao Zhang