Forgot to post a followup.
Gunsmith said the problem was my use of WWB ammo.
I told him that didn't make a lot of sense since I can repeat the problem with snap caps or with any other ammo of his choice. He also suggested that the problem was that the gun was dry. I had brought it in right after a match and a Classifier. It was pretty dry at that point, but the hangup is repeatable even after a proper lube with a snap cap in the chamber. He's done good work for me in the past, but I can't figure out this response.
I've inspected the rails as closely as I can (magnifying glass) and find no burrs or other irregularities. The indicator is free to move while the gun is in the stuck position, so I don't think it's involved (it just looked that way at first).
Since that time I've used the gun in an IDPA match (can't find 9mm ammo for the matches, grrrr....) Had no malfunctions Saturday, but when I took the gun apart to clean it after the match, the hangup was still repeatable.