Foodsaver bags are 100% good for me. However, for some reason, if I cut one open then reseal, I get about 50% failure.
You might have some issue with the heating strip. Run your hand over it, and visually inspect it, to make sure there's nothing stuck to it, and that it straight without any breaks or dips.
I occasionally make large batches of pulled pork. I end up sealing 10-20 bags in a row, then freezing. Never a problem. I also freeze sausage in them, no prob.
As mentioned above, the bags (Ziplock?) with the vacuum ports are terrible.