I too am curious about the possible newer mouthpieces.
I pulled out the ones I have - Some came with old style iolite (work FINE) some came with new style iolite and melted, some vape now sent me as replacements (scared to use) and then some the factory sent me from Ireland (scared to use). The newer ones all have the same exact hash marks as the type that melted on me. I literally have all the bags labeled so if another one melts I will know where it came from. I received the last ones from Ireland I'd say about 3-4 wks ago. I guess the newer marked ones must have come out after my replacements were sent.
Also - someone mentioned not removing the first small section of mouthpiece. I have done that from day 1 and always leave the one piece on unless getting ready to clean. I have only had the one mouthpiece melt and have since used the extra from my first iolite. I do the same with both iolites and have not had an issue since.
I also read the post about the end of butane can being possibly dirty even on the better brands. That struck a cord with me cuz one of mine was acting funny the other day, I switched to the other one and it was fine... Later it was acting funny. I realized that I had filled both of them with a can that was near its end. I vented them both and refilled with a fresh bottle after reading that post and all has been running smooth. I think there is something to the bottom of the barrel theory