Strange artifact on B&W film

Started 1 month ago | Questions thread
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b go New Member • Posts: 3
Strange artifact on B&W film

Preface: complete beginner, bought a TLR 2 months ago because it looked cool, never owned a camera before other than my phone, took a short course on shooting, developing and printing B&W and now am busy making beginner's mistakes and learning. 
These are the first film's I've developed on my own without supervision. I seem to get this strange artifact in the negatives. This one is on Ilford Delta 400, shot with a Mamiya C33 and developed in ID-11. This happened to 2 pictures on the roll

In the upper left corner there's this transparent spot. It's not a scanning error, it's also in the physical negative.
Same thing happening with lomography lady grey, developed in Df96 monobath. This happened to every picture on the roll.

this time it's more to the right. 
Am I loading the film incorrectly onto the reel or something? what causes this?
I have rolls shot later with the camera where this didn't happen, so it's not the camera.

Thanks in advance for the help.

P.S. yes I know there's dust and water marks, i've cleaned them since but not rescanned them, since I was using someone's epson v700 for these and it takes ages...

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