Vacuum bags can fail for a number of reasons. You can get a bad seal if the bag is wet or greasy, or if it's wrinkled, or if it's not positioned properly on the seal bar. In fact, it can take a bit of practice to get this right, especially for edge sealers, which can be finicky about bag placement and other things.
Another reason bags can fail is that your heat sealer is set to too-high a temperature, and it melts the bag. Some vacuum sealers allow you to adjust the heat setting, but most do not. If your seal bar is melting bags, you could try using thicker bags, but your best bet is to contact the manufacturer for advice (or an exchange).
Conversely, bags can fail because the heat seal isn't hot enough or the time isn't long enough to get a proper seal. Some vacuum sealers allow you to change the time on the seal, but if this isn't an option with your sealer, contact the manufacturer.
Bags can also lose their vacuum over time because foods release oxygen and possibly other gases. This can happen especially when doing a sous vide cook. Many meats release gases as they cook, which cause the bag to loosen up. It can also happen in the freezer.
And of course, bags can puncture, especially if there are bones or other sharp objects that could poke through the bag. Be careful to not place bags anywhere where they could get poked through by an external object, as well.
Finally, a small percentage of vacuum sealer bags are going to fail. We estimate this failure rate to be less than 1% across all brands of vacuum sealer bags.
It's unfortunate, but failure can happen.