As promised I'm back to report.
As things turned out, my gunsmith was not able to work on my 24V anytime soon so I retrieved it intending to take it to another gunsmith. However, while the rifle was waiting in the shop I kept researching & came across this recommendation: "using a hook, pull the locking block rearwards. This will unlock the barrels for removal from the receiver." Well after sitting at my table staring at the recalcitrant rifle I decided to give it a shot. Lo & behold, after some tugging & yes, cursing, I was able to get it to break open! There was no cartridge in either barrel & nothing I could discern as being the cause of its refusal to break open. I cleaned & oiled all I could reach then reclosed the action. No joy! When I tried to open it, it refused one again to open. However I now know how to open it & did so. I've looked for burrs, parts dragging, pinching, etc. but no luck thus far. Though I have nothing to compare it to, I will say that it seems to take excessive force to close the action. More than my 12ga over under & any singles I've owned. So by way of update, I can report progress but no final solution yet. I have learned that while not chronic problem with the 24Vs, it happens enough that it's well recognized so I remain hopeful I'll find a solution.