There is a small mechanical switch in the media insert slit. It can get stuck in one of its positions, forward or backward, where it should flip back to a vertical position when no media is in the insert path or the end of a sheet or roll is beyond the switch position. The last should normally indicate the end of the roll but with roll media still in the insert path like you describe there should not be a signal like that. It could be that the switch is so filled up with paper fiber etc that it hardly swings at all and just starts the insert program cycle but gets vertical again when the media transport stops for a moment. Thin roll media I gues, thicker media will push the switch more forward.
Anyway, remove the roll spindle, power off, get on your back behind the machine and look upwards at the left side (printer panel side) where a small cable connector should be, disconnect it. Remove the cover that is at the back of the printer behind the spindle, 4 special screws. On the piece you will see the switch. Test whether it stays vertical instead or swings easily. It can be taken out too, clean it and add some drops of synthetic oil suitable for plastic parts. Assemble again.
Met vriendelijke groet, Ernst
Dinkla Grafische Techniek