Before filing, when empty casing is inserted into the breech face channel, it would move in whichever direction it's leaning since the extractor claw is not holding onto the casing. This is due to the extractor depth pad not being at appropriate depth to allow the extractor claw to make contact with the casing. Casing would fall out every time with any movement to the slide...And I think it shows in how the malfunction happens, the extractor claw has no tension on the casing, so when the slide moves back during cycling, it just lets go of the casing, not pulling it back with the slide to be extracted, hence the parallel position of the empty casing.
After filing, the casing is caught by the extractor claw the moment it slides it, pushing the extractor out a bit, you can visually see this very minor movement. The casing pushes the extractor out once inserted, the extractor pushes onto the spring, providing tension and holds the casing in place, no movement whatsoever, even when I turn the slide over, and minor shaking.
I needed to take off ~.3mm for this to happen. Yours will vary, but just go slowly until the casing is able to slide in with some resistance from the extractor claw holding it flushed with the breech face. You should be able to pick up the slide, do some minor shaking, and the extractor claw would hold the empty casing in place.