I'd be tempted to put it down to the metal itself, if you're not sure of grade/origin. Simply trying different things like tip radius, rake etc. with a standard HSS tool else old style HSS square tool holder and bit are the best things to try. I've always found indexed holders & bits fine in general, but some things just won't play ball with them readily, in my experience. If you can instigate the symptoms with both an indexed tool and a HSS tool, then it's pretty much ruling out the tool and time to start checking things like bearing clearances and the like, else just ditch the scrap pile stuff and work with known grade stuff and see if that plays ball.