Thanks guys! Searching the interwebs using "AtGames Pinball, or ALP + control panel not working" as a key search phrase turns up lots of issues reported across the various VP forums, Reddit, and Steam. Found the attached at AtGames Legends Pinball OTG Direct Controller Configuration @ VP Forums which may be of help to ensure proper configuration of the OTG controller.
While the instructions are pointed towards Pinup Popper, the portions prior to that focus could be helpful in getting these types of issues resolved for PinballX users. If confirmed, may be a PinballX specific instruction could be crafted.
AtGames Legends Pinball OTG Direct Controller Configuration for Visual Pinball.pdf
In addition to providing the requested pinballx.ini, log.txt, and SetupWizard.log files, he may also want to load a text editor (Notepad, Notepad++, etc.) to see if there is an input "sticking" - would show as repeated character assigned to the key. This could possibly cause the button program to close immediately. Just a few thoughts.