Damn...that's why you ask the experts!!!
I do believe (I know, upon thinking about it and mimicking the movement you described) that I am NOT actively retracting my shoulders, both initially OR enough. So, I will start working on that, as well as reintroducing the high face pulls and wall slides into my warmup. That may be all of it right there!
I don't think the lockout portion fits for me. I definitely know it's not a flexibility issue.
I think it's that I got so into the scapular elevation part with weights overhead that I totally forgot about the retraction component. Awesome, thanks Coach!
A little more laser and a LOT more retraction, I'm thinking I'll be totally good to go.
Hopefully that answer will help many more people than just me...