Hello to anyone still reading this forum. :-)
I started this particular thread in the summer of 2019 but got pulled onto numerous other projects, then once this one was re-started I was instructed to investigate Power Apps. in the end I came full circle back to Infopath to perform the desired functions, and after re-familiarizing myself with Hilary's suggestions and her example was able to get the exact functionality I needed. The menu "tree" has been reduced from four to three levels, but for all entries there is only column used for the defect code. The Level 1 and Level 2 parts of the menu tree are bound only to xml variants and don't consume a column but still aid in navigating the 58 possible menu codes.
So all is good and working as desired right now. No problem, right? Except one, and that's the exact same bug described earlier in this thread. When saving and closing the file then reopening only the Level 3 menu drop-down- which is bound to an actual column, retains its configuration. The Level 1 and 2 xml-bound drop-downs retain nothing and have to be reconfigured every single time.
While not a "killer" issue it's a huge inconvenience because every time the file is re-opened to make a tweak I have to reconfigure 60 of these bound entries. I guess I am just checking in to see if anyone has come across a fix or work around for this particular Infopth bug.
Thank you for reading!