Learn how to use a debugger such as gdb.

You can debug MPI executables using the sys::attach_debugger() function. See the documentation of that function for details.

Useful gdb commands

To break when an exception is thrown catch throw
To break on a specific exception type catch throw std::out_of_range (This may not work on all compilers or older versions of gdb. In this case you also try setting a breakpoint on the constructor of the exception type, break std::out_of_range::out_of_range)
SpECTRE has pretty printing facilities for various custom types. In order to enable these you must add add-auto-load-safe-path /path/to/spectre/ to your ~/.gdbinit file.