Original setup for this: 1. print jobs have been running fine as long as there's filament 2. I have not been receiving the filament run-out warnings in OctoPrint 3. the filament sensor plugin appears to be running in OctoPrint 4. at least one job has run out of filament in one way or another and yet the printer blissfully "air prints" without knowing that it's out of filament 5. I attempted to run the filament through the other hole in the back of the printer with no difference whatsoever Taking the printer apart now and getting at the sensor, I see what the underlying problem is. The switch design is painfully stupid, in my humble opinion. The mechanism is a proprietary blade switch which hopes to touch the filament, only the blade is so small that it will only touch the filament if the orientation is so that it's curled in a particular way. It's effectively an inoperative part if you're lucky. There are times in which if you actually manage to close the switch it will remain stuck in place regardless of whether or not you remove the filament. At its best, it's a filament guide. At its worst, it will prevent your print job from running if it thinks there's no filament. At the moment, I have no work-around to suggest. A proper switch design would push something out of the way if 1.75mm filament is inserted into the channel. This "something" would connect a switch. Something shaped like this would work for the actuator, only the size of the particular black box is all wrong for this. You'd need to redesign the box to accommodate it. This crash sensor for the Arduino may be closer to what we're looking for but it's a three-pin connector rather than two. Ultimately, this switch may be the one to have.