Hi, thank you for contacting JustAnswer.com. My name is Russell. I will do my best to provide the right answer to your question.
The only idea that the behavior of your door suggests to me is, that it may have a defective motor with a slightly shorted winding. If, when it opens 2 feet and stops for the first time in a while, the motor housing within a minute or two of that feels distinctly warm, that would confirm the supposition that it is stopping owing to internal overheating having nothing to do with the load of the door.
But then, why would it work in the other direction OK? that I admit I cannot explain... perhaps the defective winding is not used in that direction? But you were asking for 'any idea'.
If the opener is fairly old, a decade or more, the supposition that it has a defective motor becomes somewhat more likely, I think. At any rate, either repairing or replacing the main motor might be the way to go with this case, though I admit there also might be other interpretations of the problem.
Since this really isn't much to offer, I have Opted Out, re-opening the case for other Experts' opinions.