I've had trouble with some Smisje labels also.
I tried the very cold water method on Cantillon's labels. As with your outcome the labels became mushy and wouldn't peel away without disintegrating.
Sometimes there's a thick layer of glue and two paper layers and it takes great skill to only take the top layer off but it is possible, just.
Oh well, no new or better Cantillon labels to add to my collection, but thanks to everyone who has made suggestions.