I can't say for sure without actually having the dough ball in my hands, but I'll put money on one of two things.
1) Essentially all commercially made frozen dough contains either L-cysteine (think PZ-44) or glutathione (think dead yeast) as a reducing agent to both reduce the dough mixing time and to improve processing of the cold dough. If they are getting inconsistent doses of this material into the dough (not hard to do), this might explain the unusually soft and overly sticky dough you are occasionally experiencing.
2) As you note, temperature abuse. Frozen dough does not tolerate temperature abuse well at all, and this could well be the culprit here. In either case, I would contact the manufacturer of the frozen dough and notify them of the problem. You may well need to change suppliers or go to making your own dough to get away from the problem if the dough manufacturer isn't getting flooded with dough performance complaints.
Tom Lehmann/The Dough Doctor