Standalone executable stops with no error

Recently updated to R2019a. Downloaded mcr for that release. The executable did run on R2018b, but the application code has also changed a small amount. Much of the application code is .p code (from a customer) and I previously worked thru getting all the dependencies covered. When it failed for a missing file, it gave an error message indicating that. Now when I run it from a command line, the splash screen appears, then dissapears, and after a few moments the appliction returns to the command line with no output, no message, nothing. When running from within Matlab, it runs approximately 25 minutes, displays lots of figures and output. This appears to not even be starting. I've included everything I can find in the additional files. I've added (both) mcr path to the Windows 10 path variable. (by the way, what is the difference between \Program Files\MATLAB\MATLAB Runtime\v96 and \Program Files\MATLAB\R2019a\runtime\win64 ?)

Any ideas on how to debug this ??

Mike