I've also read somewhere that, in ASOIAF, the longer someone is dead, the harder it is to pull their spirit back from the afterlife, and the longer they're gone, the less likely they are "themselves" when they return. I.e., LSH, on top of all that personal tragedy and betrayal she had gone through (or thought she had gone through), she was also dead and floating down the river for something like 3 days. So, 3 days of in-water decomposition as well as 3 days separate from the mortal plane, and all that tragedy - Lord Beric resurrected a monster which became LSH, and the process killed him.
As for Jon Snow, he's been dead for a matter of hours and you have an actual priestess potentially resurrecting him. This has a better chance of working out better.