And reading the first post it kinda sounds like the OP also has engine problems. I had under powered engine to cause bad deck engagements.
That’s what happened the first time. The next time I moved it out of the hole forward 2”Most of that style deck from husqvarna has a hole in the idler arm where the bottom of that belt guide is suppose to fit into to help prevent it from turning Just be aware that if the belt catches that guide it will bend the guide and pull on from its hole.
It’s the same belt I have been using, haven’t replaced Until I know that’s the problemBefore installing a third belt, take some time and thoroughly inspect the deck. Look at the level and angle of belt as it is routed. Remove deck if needed . Double check everything closely. As stated previously, ensure belt guide is in correct spot. Initially engage deck at lower RPM and watch, feel, and listen. Stop blades quickly if anything is not right.
Just an aside notation: A belt doesn't actually "stretch", but rather wears from the "V" side and therefore gets loose from aforementioned reason. My son had anLT 1042 Cub Cadet (MTD) that did almost the same thing. Put it away in the fall, working fine, but the next spring it kept throwing the belt. New belt was no help, so after trying everything I knew, away it went down the road.Tried again today (don’t have new belt yet) and worked like last time, came off second I moved forward. This time it didn’t make an exploding noise, just flopped off the PTO and all the other pulley that don’t have keepers. So I put it back on easily and happened again only on the PTO pulley, btw this it electric clutch. So I will proceed and buy a new belt because the old one may be stretched and with the tensioner in place, it is a little loose. Does the PTO need a keeper? It has one to keep it from spinning, but none other than that. Thanks