I don't have a perfect solution for this! Of course you have to be careful not to get oil or fat on the parts you are trying to seal. I also have had better luck with this since I stopped stretching the dough to seal it, which is to say, let it rest for 20 minutes before sealing it, then fold or braid carefully to not stretch it. Haven't you noticed that it is worse on things you handle, such as the stromboli? Finally, if it is a stuffed pastry, steam vents that don't close will let the steam out so the sides don't split to vent the steam.

If you are not vegan, you could also try an egg white brushed on the part you want to seal, it acts rather like glue as it bakes.