Hmm… from my experience with hand-held belt sanders, I’d start by looking at the overall tension of the belt drive system. If it’s slightly too loose then the backing plate spring is relatively undamped – rather more than it would be if there were greater tension – and the end result is that snatching occurs far more easily, and that it doesn’t take too much force applied to make the belt slip and stall. And at that point, it’s very likely to rip the belt, which is not such good news.
On a ‘proper’ linisher, there’s no spring in the backing plate at all – the belt tension adjustment is all there is, and as a result you don’t get this sort of problem. How easy it is to adjust or alter the tension on a cheap belt sander I don’t know, but this is almost certainly at the root of your ‘snatch’ problems.