2018-D Lincoln Cents, Mark On Reverse

Thanks, that will help me see what is going on with your coin.

Conder, no rim offset, but what ever it is extends into the design fields of the die face. Reminds me of the alignment "teeth" of the die edge...an offset die clash w/o a die in place perhaps?

Found some other ones with marks in the same spot.

I concur with all those who've concluded that this is Die Deterioration.

No it doesn't. A stutter strike is a replication of the existing details. This isn't. I still don't see it as Die Deterioration as Mike said, but what else? (BTW, just who wrote the info on "stutter strike?)

This may sound crazy but it almost looks like this sequence.

Rev was mis-aligned as hammer die.
Collar clash transferring part of UNI tot he edge of the collar.
Collar counterclash transferring part of UNI from the edge of the collar back to the die but offset.
Rev die re-aligned but face slightly out of parallel with the obv die.
Coin is struck showing collar counterclash with missing rim from out of parallel dies.

I found about 2 dozen out of two boxes of pennies and maybe 6 have the same issue. I'll upload pics in a few hours

Die issue, again, what?