The worst part is that the glue is thermoplastic and thus does not set up into a heat resistant mode. Further, there are some things to which it doesn't adhere well.
So,
like every single adhesive in existence, it has characteristics and limitations? Shocking…
Of course it’s thermoplastic. If it were thermoset, the glue gun would be single-use (if that). Being thermoplastic is neither a feature nor a bug: depending on the application, this can be a desirable quality or not.
And there is no glue in the world —
none — that adheres to everything. That’s why they make thousands of different kinds of adhesive systems. (I say “systems” because many high-performance adhesives involve using pre-treatments, primers, accelerants, etc., and come in many forms: liquids, gels, pastes, putties, as tapes, sprays, etc)
You have to choose the right adhesive system for your application. If you need heat resistance, then hot melt is
obviously the wrong kind, and you’d likely end up with a silicone or epoxy.