Another thought... perhaps when you press the sealing bar, there is too much pressure and the snorkel tip is getting trapped. It might help to seal, release the arm, then re-seal again just a few millimeters further back as "insurance."
We also suggest you can press the closed end against the inside wall of the fridge when you put it on the rack. Holding it there just the few days it takes for the bond to form, then moving it to leave room for air to flow has worked. As I think you understand, once the majority of the DrybagSteak has bonded with the surface of the meat, the process is well on its way. It is not a "vacuum" you need so much as simply really, really good contact.
Let's hope we can find success for you!

not folding the bag over when inserting was the mistake i made with my first run. i was still able to eventually get a 'good-enough' vaccum seal.

i'll definitely fold it over on my 2nd try, and i'll be trying a "raft" like RRP put together...thanks for sharing!

Success!!!
Thank you all for the suggestions for a rookie. And a special thanks to Thea for sending some more dray bag material after I blew through my initial batch - excellent customer care!
I now know what the problem was and I'll share for any other newbies out there. I was getting air back into the bag as the snorkel retracted because the seal bar wasn't getting even pressure across the entire strip. It is critical to apply even and moderately heavy pressure across both sides of the seal bar. I had been applying good pressure to the bar, but not evenly - thus the edge had just enough of a gap to allow air back in.
I just sealed an 11# strip loin and it worked perfectly. I'm also a strong proponent of the 'raft' accessory. The only question remaining is... Do I have enough will power to wait 28 days or will I fire up the grill after 14?

Glad to hear of your success! As for going the distance of the 28 days I say it is well worth it and in fact a shame not to. Just place it on your bottom shelf and forget it, though do mark your calendar!