Another thought, Mike, are you using a #4 setting on your Sinbo? Also having the meat a bit moist will work in your favor as it will make the bag tend to stick to the meat when you manually press out air. Also did you fold back the bag so the inside didn’t get juices and grease on it which can hamper sealing? Before I even start to seal I manually press. pinch, fold whatever as much air out as I can – and then again after I’ve done the two diagonal seals. Then be sure the unsealed slot between the diagonal seals isn’t too big or you’ll be fighting air trying to get back in. Here’s another post in which on down I show some before and after pictures that may give you some pointers.