Ive used both plastic and SS reels, and I prefer the plastic much better for some reason. I have used some that work flawlessly and others that just dont cooperate at all.
I suggest you wash your equipment with a tiny bit of detergent and let fully dry. they use a pencil and run it through the tracks to "lube" it.
Take your time and guide the film into the reel when ratcheting with your thumbs. for doing 120 defiantly get the larger take up plastic flanged ones.
I always add just a little bit more of each chemical, if it asks for 10 or 12 oz. I put in 12 or 14 oz of solution for a single reel. and also if you are doing a single reel in a 2 reel tank, always keep the one with film on the bottom. and agitate vigorously, flipping and rotating as well regularly.