The tell is almost always sound before it's motion: a rhythmic squeak or grind that gets louder as the door moves, one thump per rotation if a roller has flat-spotted. Steel rollers from the early 90s wear this way - they don't shatter, they flatten on one side and then hammer the track every time they roll over that flat spot.
On the newer end of DeSoto's housing stock, nylon rollers fail differently: they crack or shed small chips of plastic near the track, and the door starts to hang slightly crooked at one corner before it ever makes noise. Either way, catching it before the roller comes off the stem entirely saves you a stuck door and, sometimes, a bent track that costs more to straighten than the rollers would have cost to replace.