Checking my stores of mylar bagged dry goods. Did not vacuum seal. Most bags have drawn in like they had been, some have not. What does generally mean in both cases? All 1 gallon sized bags with oxygen, some with moisture absorption too depending on food.
There are several steps I would recommend you follow while sealing your Mylar bags. Firstly, double-check to ensure there are no pinholes or any other issues/damages. Secondly, wipe clean the inside bag lips or any poured food residues as they must heat bond together cleanly. Thirdly, add the O2 absorbers and seal the bags. Last but not least, make sure you are using good quality bags. I’ve been personally using Mylar Foil Bags and O2 Absorbers for quite some time already, and I’ve never encountered any issues and am pleased with their quality. Also, they offer a competitive price.