Since it's doing it in two different decks I'd suspect the tape is requiring too much force to get to the end and it's triggering the STOP. It could be a few different reasons, Coke dried on the tape, the plastic hub is damaged and doesn't turn smooth, the cassette case has heat damage or other similar factors. You might be able to FF/REW it to working condition after a few times or there might be some "lube" you can put on the parts. Luckily it's the tape and not the machines.
There was a video on YouTube about relubricating cassettes. Sorry I didn't make a note of it at the time.
