I'm going to keep cycling my remaining 6 snap caps and see if they also end up damaged. maybe I need to polish the feed ramps like others have mentioned.I have similar snap caps and they cycle just fine in my RDB-C. Granted that I have already ran about 200 rounds of XM193 in my rifle at the range without any issue.
One way to determine what could have caused the damage is by slowly let go of the bolt when doing manual cycling. You should not feel any resistance with the bolt movement until the very end of its travel where it locks in to the barrel extension. When I carry out this action too slow, sometimes the bolt will fail to lock properly. Good thing is on RDB when the charging handle is unfolded and is locked into the operating rod, it can also act as forward assist.