Assuming both were developed by the same lab, I would probably run a short roll of B&W and develop it myself, but next closest idea would be shoot the cheapest color you can find and get it developed somewhere else. Then see if the problem persists. Or have you had recent good results from your lab with another 35mm camera? That is, it might not be your end.

I just dug my AE-1 out and can't say I have any "Aha!" moments looking at it. There is a film reminder widget on the back that holds a box top. It appears to be attached by some sort of rivets or plastic studs -- is all that in place? (Since it is behind the pressure plate, I doubt that could be it, but we're being rather challenged here!)

There are three small screws in the cassette end, two in the body and one in the cover -- are they all there? (Again, I think this is very unlikely, as the film is inside the can at that end.

In the take-up spindle end (right end from photog's perspective) there appears to be thin foam on both the body and the back, next to the hinge. On mine (unused in about a dozen years), there doesn't appear to be much left to flag that those were seals! What does catch my tired and ancient eye is that there is a gap in the tubular roll that forms the hinge, where I can see a shiny chrome pin/rod of some sort. I suspect the gap is access to retract the spring loaded pin to remove the back. It's about the right distance from the edge of the film to create your problem -- but being it's next to the take-up spindle, I would maybe expect the effects to vary a bit as the spool fills and the diameter changes. If those seals mesh, it shouldn't be a problem.

Assuming all the exterior components -- covers, shrouds, whatever are undamaged, it's hard to see where things might otherwise run amok. Does your camera show any signs of damage -- bent metal work or fumbled repairs?

My goto Canon FD is an A-1, so I don't have much AE-1 experience to go on. Shortly after my dad died, mom gave me his AE-1 and I did put a few rolls through it, but we're talking 1998 or so, and all was well at the time. I'd say the seals in mine definitely look a bit sketchy now.

I find it difficult to suspect the lens end, but do you have -- or can you beg, borrow or steal -- another lens to try a few shots?

Edit: There is a strip of foam across the front of the ground glass area that serves as a mirror bumper -- is that intact? (I'd think your strange spot is too sharply defined to be from that but since we haven't accounted for it .... )

(Hey! Maybe all this thinking will prevent Alzheimers! )