I solved this by hitting the back of the slide to put the pistol into battery an fired the round.
The slide then functioned and the brass ejected.

Would love to figure out what was going on though…

I should run some more rounds through with 5.5g of silhouette to see if this can be reproduced.
What I am more likely to do it to go to the 6g that I was using for jacked bullets and see how that works.
Having ammo stuck in my gun scares me from a tactical standpoint.

Any thoughts still much appreciated.