Update. Just got this email from DL (and my name was spelled wrong due to common spellcheck error, so it would appear a copy/paste deal and not 100% automated). Weird.
Also realizing now that this probably wasn't the best thread for this story - I originally thought it was sched change related. Oh well.
Dear Mr. Lee,
We wanted to let you know that unfortunately your seat assignment on
Flight XX on DATE has been changed due to a technical seat
duplication issue. We've done our best to give you a similar seat; your
new seat is 05A.
We know you have seat preferences and are really sorry we had to change
your seat. You're welcome to review your new seat assignment on
delta.com or the Fly Delta app where you can view your seat and select
from other available seat options.
Again, we apologize we weren't able to honor your original seat choice
and for any inconvenience this may cause. We're grateful for your
SkyMiles loyalty and look forward to seeing you on board again soon.