Skipped timing I have seen from the following:
(1) A/C belt came off and into the timing cover while running. Usually when the crank pulley is separating.
(2) BS belt broke and got into the main timing belt.
(3) Back BS bearing seizing, which in turn causes the oil pump sprocket to turn hard and occasionally skip. Eventually it locks and shreds TB. Just happened on the mighty max.
(4) Timing belt adjuster is bad. The tensioner is actually the pulley, since that is what you actually set the tension with. The hydraulic adjuster maintains tension during varying load conditions. This is the most common as most people don't know they are bad. If you can collapse it with your thumb, its bad.
Wiz