I have a digital weller that I can change the temperature on. I've tried anywhere from 550 F all the way up to 850 F and I usually run into the same problem. But maybe that's just me cause the last time it happened I did smell something weird which was probably the adhesive getting too hot.
The solder I'm using is canfield silver gleem which melts at around 450 F. Sometimes it takes a while to melt and I have my iron in the same place for a while, maybe that could be burning the adhesive even though I don't have the temperature cranked up?
The foil itself is not very sticky and it's pretty thin but it's also rated pretty high by people on amazon who use it for stained glass which has me sorta confused given the problems I'm having with it but I also just started so I don't know what good foil looks like.