I compiled the Win32 version of my program on macOS which usually works with no dramas. This time, however, the executable failed to do anything when run on Win32 systems (I tried everything from XP through Win10).
On a wing and a prayer, I compiled a Win64 version. When running this on a Win64 system, I received an access violation error dialog about a method and the program did not run (I chose OK instead of Abort).
Going back to the source, I had a dangling method in the Windows-specific part of the source code. Once I removed that all was well again.
Recorded for posterity lest anyone else encounter this odd phenomenon.