I don't see anywhere where you posted what year vehicle you have.

The accessory belt idler pulley width was increased somewhere early in the 2G production and that helps to have the wider pulley but ultimately if all else is good the culprit is almost always an alignment issue.

You can't see it visually but in my case I could stretch a thread tightly across the face of the pulleys and see that the PS pump pulley was leaning inward. My belt would hop off anytime I de-accelerated if I had been at high revs in the moment before backing off the throttle.

My friend with a 98 TAlon could hop a belt on command with a blip of the throttle. He noticed a mis-aligment of the idler pulley and added a small wsaher under the bracket to set it straight. He hasn't thrown a belt since that day.