I know this is an older question but here is a method I developed over the years:
I use nonstick pans but I‘ve done it also in stainless.
I use a small amount of oil and warm it to thinly cover the pan bottom.
I add the potstickers, tight but in a single layer, and cover with hot water about 2/3 of their height.
I bring it to a boil moving the pan slightly back and forth just to move the potstickers in it. I do not use lids.
I boil them, turning them halfway and moving the pan regularly to not let the dumplings settle and stick.
I continue until the water nearly evaporates and slimy dough residue starts showing in the pan.
I increase the heat and now I move the pan in a circular motion until the potstickers “pick up” all the dough slime.
After a minute or two the dumplings sit in clear oil (just coating the surface). I sear them on three sides until they start showing crispy surface.
I use 2 pans simultaneously to make about 30 potstickers. This method requires staying nearby pretty much the whole time (once they are frying you can step away as they will no longer stick but you still have to watch the browning).
The dumplings are soft and juicy on the inside and crisp on the outside. After using several other methods I settled on this one and my diners love it.
(I understand my answer is broader than the narrow question of why the sticking problem recently emerged with a stainless pan. Recent scratches in the pan may be the cause but I found that moving the pan and making the potstickers slide prevents the sticking even in pans than no longer have perfect surfaces, stainless or nonstick).