Perhaps if you take one of the bags you just sealed that filled with air and immerse it in a sink full of water and squeeze you can see where the air bubbles are coming out of the bags.

It is either not heat sealing properly of maybe you have a bad batch of bags that have some small punctures in them.

Sounds to me like you are trapping air in the bottom of the bags. It depends on the consistency of whatever you are sealing, but for most foods - especially meats - I always fill and then using my plastic glove covered hand or a spoon run a channel down each side inside the bag before sealing. Also be sure to wipe the inside lips of the bag before sealing. Works for me! 

Here is my personal experience from the last few years so vac sealing. 
I find that when I use the rolls to make custom size bags, I have more bag fails. 
I dont use the FS bags or rolls anymore. I buy from the sweet attack online. 
I also find I can't use the machine in rapid succession. Meaning, I can do a couple bags in a row then it doesn't seem to suck out as much air. If I let it rest for a couple minutes it's fine again. So now I bag as I'm filling because I'm not standing over the machine loading in bag after bag. I can go continually this way for a long time. 

I had what sounds like the same problem.  I actually double seal in the same spot.  On my model, it will not seal again until I open the lid and close again.  So I just seal, open, close, seal, and move to the next bag.  I do this for both the first seal (when cutting a bag off a roll) and the second seal when vacuuming. 

I had the issue for quite a while and couldn't figure out what was going on. Was it the cheap amazon sealer? amazon bulk bags? nope. I think it was the same thing @pab mentioned, the moisture was compromising the seals. I was waiting for the machine to auto seal after the air was removed. It was removing so much air that the moisture eventually made it to the sealing area and messed everything up. Partly freezing before sealing makes sense!

I always double seal. Same as @OhioEgger

Since your FoodSaver is automatic, maybe seal in the same place twice like @RiverRatSkier suggested? MyFoodSaver is a different model but seals automatically as well. I see you have a moist food setting on yours.  I always use that setting when I seal my bags and have had your problem maybe 3 or 4 times in the three years I have had mine.  If you are sealing food that has already been cooked it probably has more moisture than raw food. Even raw meat will have moisture drawn out by the suction which is why I suggested par freezing, it doesn't need to be frozen solid. On the moist food setting the vacuum is not as strong so it is less likely to pull moisture all the way to the sealer bar.