It was used incorrectly then. PAM and NIX solution is pretty much identical. Just look at the ingredients. And the only one that matters is Permethrin. Its just a different base, from Water to Aresol.
With NIX if you can get it make sure your substrate is always treated. Always Use paper and treat a few extra sheets for when you change, it All instructions are the same, Liberally put on snake. Better part of nix is it can go on there head/vents, Aswell keep water bowl out for 24hours to let it dry so snake doesn't drink any. If you notice snake soaking leave water dish out till mites are gone.