Popper alternate program (ALTEXE) missing
What it means
These games do not start from the frontend.
Why it happens
A game can name an alternate VPX program (ALTEXE), started from the launch folder instead of the default one (PinUP documentation, VPX emulator page).
How Pincab Toolbox detects it
The game is visible, its ALTEXE field names a program without spaces, the script uses the default ALTEXE line, and that program is neither in the launch folder nor in the PATH.
Check your own pincab
Pincab Toolbox is a free Windows scanner for Visual Pinball X and PinUP Popper. It finds and explains problems like this one. No account, no telemetry.
Download for freeCovered: Visual Pinball X (10.x) and PinUP Popper. Not covered: Future Pinball, Pinball FX, Visual Pinball 9 and the other frontends (PinballX, PinballY).