We had a lady at my last IDPA match that was having no end of trouble with FTFs and FTEs. They finally disassembled the magazines, brushed them out and put a very light coat of oil in them.
That fixed one, but the other appeared to have too much metal near the lips. They compared it to someone else's mags that were working fine. Visible difference. Both looked like normal magazines, well finished edges, no burrs. But the ones that had problems were visibly deeper (front to back) along the lips. Like the sheet metal was not trimmed back at the front edge of the lips. Without a good one to compare it to, it would be hard to identify the issue.