Filter Keys enabled
What it means
Flippers wired as keyboard keys can react late or miss presses.
Why it happens
Windows Filter Keys delays or ignores short and repeated key presses (Microsoft, FILTERKEYS). Its shortcut is holding Right Shift, VPX's default right flipper, for eight seconds.
How Pincab Toolbox detects it
Windows reports Filter Keys on, with a non-zero wait or bounce time (SystemParametersInfo, SPI_GETFILTERKEYS).
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).