Looks like it's hanging up on the lips.
All - - -
Thanks for the advice.
Owners' manual had nothing that addressed this. Pushing follower down didn't have any effect. It looks like the bolt is jamming on the lips of the magazine, and it does that not matter which direction the bolt is going. That is, if a magazine is inserted, I can't close the bolt, and if I insert a magazine after closing the bolt, then I can't open it. And yes, I've tried different magazines, including GI and Magpul.
Bummer. I really like the overall feel of this gun... Except for that glue-stick buffer pad.
- - - Yoda