In mid-November, I purchased a seat in Premium Select (for SEA-CDG) for a flight in mid-January and, with the seat map wide open at that time (because it was two months away) chose my favorite PS seat: a bulkhead window, in this case 20A (in an A330). There has been no change of equipment since then. I have made it a point to check the seat map every week or so to see if there are reasonable upgrade offers to D1. But when I checked the seat map today, I see I have been moved to 20C (bulkhead aisle in middle section). Granted, it's still a bulkhead, but really like bulkhead window.

What's up with this? Is there anything I can do about it other than hope that the 20A or 20J passenger gets upgraded and I can reclaim one of those seats? I thought that seat assignments, when confirmed, were confirmed. I suppose the one good thing that COULD happen is that the "center-center" seat, 20D, goes empty (it is unassigned as of today), and in that case I suppose I'd say a bulkhead aisle in the middle section with an empty adjacent seat is preferable to a bulkhead window. But I am not optimistic that this will happen. I've flown international PS about 10 times, and on every occasion, the PS cabin has been 100% occupied.

Sounds like you were moved to accommodate a disabled passenger as they tend to be assigned bulkhead seats (can vary by aircraft, but in general bulkheads are prone to this). Or could�ve been an ultra-high status pax traveling with a companion that an agent moved to sit next to in the �B� seat. (Not policy or a published benefit, but does happen from time to time). At any rate seat assignments are subject to change, but I do agree it�s frustrating when it does happen.

Day of seat swaps can also be due to deadheading crew contractual seat requirements or inoperative seats.

Lastly, good ole Delta IT is always a possibility as well.

Likely disability accommodation. Bulkhead must be given to certain disabled passengers upon request.

And I believe there is a note when you select bulkhead seats that you may be moved for such an accommodation

OK, I understand. But if I was moved from 20A to 20C, that would imply the disabled person could have been placed in 20C (in fact I would think that a disabled person would be better served by an aisle seat). And if the disabled person needed to sit next to a companion, why couldn't the companion go in 20D? (which is indicated to be empty).

Most likely person with disability + companion. It makes a lot more sense to put the two of them in A/B by themselves, than to put them in the middle with one in the middle seat. Companion may need to assist the disabled person. Also, there could be a service animal involved here, and in that situation this gives them more room (no other passengers in 20G sharing the space).

yeah you're not ever going to get a phone agent to tell you why it happened, it just does sometimes and you'll hear people here just make up all sorts of wild theories. it doesn't really matter, once this happens the chances you get a phone agent to change it back are very, very near zero

I did actually call. The agent had no record of my seat being changed, but first hypothesized it could have been due to the schedule change (there was a trivial schedule change of like 10 minutes), and then said maybe Air France might have had something to do with it (it is a Delta itinerary booked with Delta, with a connection to AF at CDG). She also said there is really no kind of "standby" kind of thing she could do for me to put me in one of my preferred seats should one open up. She suggested to just keep monitoring the seat map in case something opens up, and check with the gate agent on travel day.

I don't blame the agent for this. But it would be nice if involuntary seat changes are made by the airline, some sort of a note explaining it would be nice. Though if it is because of a disabled passenger, I suppose it might be some kind of HIPAA violation or would be deemed to be insulting to the disabled passenger or something. Because everyone is sensitive these days.

HIPAA doesn't cover airlines. It's a privacy thing. No one else has the right to know your personal business. People want answers for stuff all the time, but I'm not sure how providing that info benefits DL. "Someone is disabled." Then you get on the plane and decide that the person isn't disabled enough and make a stink about it. "Accommodate a VIP" Then you complain that your money matters less. "Security" Then you get on the plane and harass the security people. There's nothing in sharing that benefits DL.

Schedule changes can also do it. While the plane may not have changed, seats can be switched if the plane changes at any time, even for a moment on SCS.

You can set a seat alert of Expert Flyer to get an email if one of the seats you want opens up. However, EF only checks at intervals of AFAIK undisclosed length, although the checks get closer together as departure approaches.

On an widebody bulkhead, if available, I always take the HJ side of the aircraft not AB. Seems like that rare disability bump case will be seated as close to the boarding door as possible.

Excellent advice! I'll do that in the future. I usually choose my side of the aircraft based on which side of the aircraft will NOT be in direct sun, but in this scenario, I would prioritize the lower probability of being bumped.

I normally do the opposite. This way I can close window shade and not be blinded.

I am on an A321 (I think CEO not NEO, it just says A321).

My wife is in 2A, I was moved from 2B to 1D (separate PNRs). The cabin is full, the flight is next week.

If thought, 1D is the worst seat in the First Cabin. I have a bad knee and can't fly that long without the legroom. Or is there plenty of room? The agent said that's where they put folks with a fused leg.

Delta Comfort is full except for a middle bulkhead. The other flight times are no good (leaving at 7am, or arriving after 11pm). Other than setting alerts in EF, I"m guessing I'm SOL? Any recourse to get them to move me back?

I see why I might get moved out of a bulkhead but why did I get moved to a bulkhead?

ETA - I was told I was "moved by the system" to accomodate a family - but it doesn't really make sense. They said if I cross referenced my resrevations, it wouldn't have happened. Lesson learned.
They say only the gate can move the seats now.

I had this happen to me last year on a flight to from DTW to CDG, but Delta sent me an email informing me of the change:

"We wanted to let you know that unfortunately your seat assignment on
Flight DL98 on March 25 has been changed due to circumstances beyond our
control. We've done our best to give you a similar seat; your new seat
is 8A.

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."