Mingaun, I used to have this problem with the film becoming hard to insert into the reel until I found out the absolutely definitive solution to this problem. I use plastic reels, like you. That means that the entire length of the film slides inside the reel during the movement.

(I don't have stainless steel reels, but I understand that with SS reels the film does not "advance" inside the reel from the outer edge, but is instead "spooled" around the reel rocket from the inner part, but I might be wrong).

I found that my problems were due to two mistakes in cutting the edge to insert inside the reel.

The first mistake was to cut the leader with a U shape (almost a V shape). The "shoulders" were much lower than the "head" of the tip. That's bad because when you use a small tank like the Jobo 1500 series, when the film advances inside the reel it will be more and more bent and the "tongue" protruding beyond the margin sides will touch the film on the outer reel's groove.

The second mistake was in cutting the corners of the film. If you watch YouTube videos you see that people just make a 45 cut taking out a couple millimetres at each side of the leader. When I did that, I had problems.

Now I cut a very small but very "rounded" edge. Not bigger than a few millimetres, but rounded. Take inspiration from the way the film is factory rounded where the leader (the narrow tip with only one perforation) ends and the film begins being full heights. You will notice that the film margin is rounded. I now cut from that point, a very flat cut, and on the other side of the film I "replicate" the same round cut as the one factory-made on the other side.

The film flies through the reel!

(I'm sure this helps )