Hello Sean, hydraulic lock is an interesting theory but I don't think it would make the belt jump as the crank is the driving pulley so if it locks it should just stop driving the cam. It may bend a con rod though. I would be looking for foreign objects in the cambelt area. Hope this makes sense (I think it does in my head).
Also looking at your fuel trims it looks like you have a bent no'2 inlet valve (+2.99 on no.2- ecu trying to speed that cylinder up but when it sprays, fuel is being lost into the inlet manifold as no.4 is on the inlet stroke causing that cylinder to be on -2.31). Just my theory. Hope this helps, Alan.