I have the Foodsaver FM2100. Ive noticed on the first couple of defrosts, that the bag seems to have air in it after the meat thaws. Like you can move the meat around in the bag with some small air pockets. However, at the time of vaccing it, it looked perfectly air tight and the meat was locked in place. Are these bags taking on air or not being sealed properly, or does something happen during the thawing process? TY guys.