Hi Cameron,
Are you still having issues with this? I have the UK equivalent of the Ethos, the Rafaello Power Bore and have exactly the same problem as you. I put some 32gr cartridges through mine (50 albeit) and had 0 failure to feed. I don't understand why a 32gr works flawlessly and a 28gr doesn't when the problem seems to be a pinching between the walls of the breach and carrier latch? (Not sure of the US imperial equivalent). Did you get the cartridge latch changed? I might send mine in to have it changed.
Thanks
Ryan