Tray developing - strange marks/scratches on film base

[Valleyboy]

I recently started tray developing 4x5 film (have done 8 sheets so far) and noticed these strange scratches/marks on the film base side of the negs (not on emulsion side). Anyone know what could cause them? They don't look like linear scratches, more like the film base is cracking or peeling. There are smaller marks around the edges of the film, and a few large spots in random places.

These appeared, in various quantities, in all six negatives I processed. You can't see them from the emulsion side so I'm hoping they'll print fine, but would like to avoid them if possible.

Could these be damage caused from scratching along the bottom of the tray? From the film holders pre-development? Something during the drying process? Something else? Below are the materials and process used:

HP5 + (all are from the same box of film)
3 min pre-soak
Dev in Rodinal 1+25 8 min (2 negs at a time in an 8x10 tray, shuffled by lifting one neg out of tray, moving other neg forward to top of tray, and placing removed neg into bottom of tray, once every 30s)
1:4 white vinegar:water stop bath
Ilford Rapid Fixer 1:9 for 5 mins (similar agitation to above)
approx 15 min rinse in a large tray with a Kodak tray siphon, final rinse in a separate tray with Ilfotol
Hung to dry w/alligator clips

Curious as to what this could be. Once again, the emulsion side of the film is flawless - no scratches or marks. These are only appearing on the film base side.

216591
216592

Thanks in advance.

[Michael R]

I suggest you waste two sheets of film running through your process with the lights on. Inspect the base side of each sheet first. Then go through the full process and inspect again. This might help narrow it down.

[Valleyboy]

Thanks Michael - that's a great idea and I may do as you suggest. Was hoping before I burn a few sheets of film that someone may have come across the same issue.

[Vaughn]

They look like it might be film corner damage. One standard method is to slip the bottom negative out of the tray, lay it on top of the stack and press down to get it under the liquid.