Hunting down a lightleak

Hello,
I am using an Alden 74 for loading my Ixmoo cassettes. I just processed a film (Kodak Double-X 5222), and, in the middle of the film I have a big lightleak (see first picture attached).
I know it’s not coming from the camera (Leica M6) as I didn’t have any issues with other film done the very same day. I don’t think it’s coming from the cassette itself the only culprit left would be the bulk-loader.
I tape the door closing the cassette receptacle, the springs which hold the door are a bit weak and the door kind of move a little bit, so to be sure it closes properly I put some black electrician tape all around the edges.
I have noticed that the knob for closing back the ixmoo cassettes doe’s come back all the way back in position (see the second and third pictures) could it be the source of the leak? And if yes what would be the best solution to solve the issue?
Thank you very much in advance for your time and help
Wishing you a beautiful day
Alain
PS: English is not my first language, so my apologies for any grammar errors and please do not hesitate to ask me if I am not clear