Maximum number of MPI processes

Hello, 

I would like to ask about the maximum number of MPI processes supported in Intel MPI 2019.0.5

Case in point, we was conducting massive parallel tests on Knight-Landings cluster. The total number of cores was 4096 x 64 ~ 260K at which the test hung without updating output file for extended period of time. We suspect this may be due an intrinsic limitation of Intel MPI.  

Clarification is much appreciated. 

Regards.