bulgarian 5.45 on ohio reciever

what would cause a round to extract normaly but the next live round gets loaded crooked and gets jammed and sticks out of the action. this was with a steel tantal mag half full

im guesing it is a bad magazine?  reason i ask is i just got this rifle back from being repaired  (carrier was smashing into ejctor rail, deformed sfter 1000rds  and i had several failures to eject (cases stuck into chamber)

i put 300rds wolf 5.45 fmj and 60rds silver bear fmj thru it today to verify it was fixed. i only had this one problem