I doubt if the threads were corroded, especially that quickly. It was probably just a faulty jag. It happens.

That is one reason the use of a good strong range rod is something I swear by. I have a stainless steel range rod with a large T handle that was custom made, and it works great. My old Thompson Center Range rod finally wore the threads out. I thought about re-tapping it or just epoxy a permanent cleaning jag to it. I might still do that. That Cain's Super Rod is a great rod. I bought one for one of my flintlocks. A real quality item there.