Hey there,
Definetly find some one with a bore scope to check out the chamber....
Had a similar situation with a my cousin's new tikka t3 in 300wsm just the other week, first shot out of it and the brass stuck in the chamber, tapped it out and took a look for excessive pressure signs and everything looked fine, however it had some shiny marks around the case head much like your picture... measured the outer dimensions on the case thinking maybe it was a wonky chamber but all was good... fired another round over the magnettospeed, speed was what we expected but had a stuck case...
Looked with my borescope and found the chamber had a whole bunch of scratches in it, so bad that you'd wonder how it would pass quality control.... looked like the Finn running the reamer was a little cheap with the cutting fluid and got some chips floating around in there chowdering things up..it was obviously bad enough that it wouldn't let go of the brass....
Anyways nothing a power drill, some 600 grit sand paper, a broken graphite arrow shaft, lapping compound, flitz polish paste and 45 minutes couldn't fix... polished the crap outta the chamber and now it cycle like a champ... if that's not something you are comfortable with send it back
Let us know what you figure out...
Orch