I read in somebody’s blog recently that he had had trouble in getting the film to load into the spiral and had ruined a film. I must admit that I have never has such a problem and I can only assume that the instructions in the manual had not been followed to the letter.
The instructions in the 1964 edition of the 35U manual (available under DOWNLOADS above) are probably the best. There are several stages that could be of critical importance, including cutting the film leader off absolutely at right angles to the length of film and between perforations, then cutting a bevel off the corners, and turning them slightly inwards. The manual does not explain what inwards means but I turned them towards the emulsion side. It is equally important to attach the clip in the centre of the film. There is a recess in the tank to hold the clip in the centre. However, I preferred to close the clip with the cassette and spiral reel out of the tank. That way, I could check that there was an equal width of film on either side of the clip and that the film was pushed firmly against the back of the clip.
Before I sold my 35U, I did see what the effects were of not getting the clip central and of not cutting the film off at a right angle. I used an old length of film and watched what happened with the lid off. Sure enough if the film was skewed in the clip, loading into the spiral could fail at various stages in the length of a 36-exposure film.
Those with an Essex tank will know that the preparation of the film and attachment to the band are different. It is more of a hassle but in that tank the clip (which is not a clip but a buckle) really does hold the film in the centre.
I think it is a case of read—and follow exactly—what it says in the manual.