It could very well be that your scion were not good.
I don't think your rubber band were too tight, I use electrical tape. No, you shouldn't loose the rubber band until well into the season. I take off the tape next spring. It would be good to have some scion put on from a different source,..just to compare.

I'm not sure about potential scion/rootstock incompatibility issues, but I have experienced the pushing scions which then simply collapse. In those cases I believe there was not sufficient cambial contact for a good union. The apparent "flush" of the scion is just from energy stored in the wood, just as scions kept for a long time in the refrigerator will slowly start to push out their buds. Makes it hard to know when you should just abandon an effort and regraft :-(

I've got two plum grafts out of eight plum/peach grafts that are making me nervous because of their lackluster leafing out. Makes me wonder about them, and the backup wood in the fridge is not getting any fresher.

I would suspect the scion wood too.

I think that it might be possible to wrap the graft union too tight with rubbers. I got carried away for a while wrapping mine and had a few failures that might be attributable to that, and the bark was quite dark when I finally removed them. And I could clearly see the imprint of my wrapping. The bark appeared compressed and shiny. But I never had the problem with pears- just apples.

Good luck,

Mark