I have been told that 'masz problem' just used on its own like this is considered rude and unfriendly. Can any native speaker confirm? I suppose it would depend on the context and situation.
It depends on context and intonation. It can be used humorously. "Masz jakiś problem?" is quite common and casual. Surely, you shouldn't use it when you don't well know a person you talk to.
Yes it is offensive for example when you walking on the street and start conversation with "Masz problem?" To strange person. Its also depend on intonation :>