Sous vide air bubble, still safe to eat?
Air in the bag can be a result of two things: (a) you did not properly eliminate it, or (b) bacterial growth.  The main problem is that the portion of the protein that has floated above the water will not be at the same temperature as that which is under the surface. We don't know what portion of the meat was above the waterline, nor for how long. So, I won't make any guesses about safety or quality. Given your description it is difficult to determine whether your issues is related to (a) or (b)...or maybe even both, if you did not notice floating immediately.  In the future, firstly make sure you seal properly, by using a vacuum machine, or barring that, submerging your bag, which has been sealed most of the way, in water to force the air out.  At the last moment, seal the rest of the way. You can inhibit bacterial growth on long cooks at low temperatures by either giving the protein a quick sear on all sides, or a 10 second dunk in boiling water.  If you are using sturdy vacuum bags, you can dunk in boiling water after you bag the meat.