If you have worked extensively with any robust PB application you will know that 99% of your objects are tightly coupled or depend on many other things like their parent, related children, NVUO services, global variables, etc. So trying to remove (which logically probably defeats the application) or move these to another new application test bench would be very excessive work.
The better (more effective ROI) recommendations (IMHO) would be to:
a) Use the PB debugger and step through the code where it crashes.
b) Use the PB Trace feature (command line)
c) Look at the current applications warnings in the PB 12.6 compilation vs PB 11.x's.
d) Comment out suspicious code
etc
Note: I still cannot run my frameworks & example applications in PB v12.6 because the migration adds objects and changes my code-line. The only way to effect a running application is for me to manually edit the source code. I kid you NOT! 