- Edited
Android phones have a special controller that can work in active and in passive mode.
It can also change it's mode, for the various functions like "file tranfer" (MTP), "digital camera", "usb tethering", "webcam" (and "debugging" is a separate one too I think).
When using USBGuard on Linux, normal passive devices work when allowing them temporarily. But if you connect your phone and temporarily allow it, MTP doesnt work.
Does the USB controller change something again, after you plug in with data mode, and want to use MTP?
I dont need to allow a separate device again, I just need to permanently allow the device in "file transfer" mode and it works with MTP.
Maybe the controller shuts down for a short time, or reconfigures itself?