I would call DL back and ask to speak with a supervisor. Whatever the reason, there has to be a reason. Every action taken on a PNR is logged and DL can untangle that.

If this does not work out, I would send a note to DL with the specific fact that you were told that a supervisor had downgraded you manually (thus hopefully meaning that you won't get a cut & paste answer) and asking that DL investigate why the supervisor did this.

Speculating about who and why is not going to do anything.

I have to admit that I was such DYKWIA once and it worked for me (I have no idea if they removed upgrade or just overbooked the cabin).

I can not always afford to fly in paid F, but when I do, I totally expect a seat to be available for last minute changes and missed connections at least a few hours before departure, unless of course F is sold out. I think IM got much better, but in the past it could happen that upgrades took all available seats 24 hours before departure.

I have never heard of DL downgrading confirmed F pax, upgraded or not, because someone wanted to SDC. Nothing about buying a first class ticket on one flight entitles you a first class seat on a different flight (there is no such thing as guaranteed same day change). At best your claim to that seat is equal to the claim of the upgraded medallion because you are both using medallion benefits to access a seat that you did not pay for, so whoever got it first should keep it. If DL wants to oversell an F cabin and offer compensation for volunteers or to IDB pax, that's a different story, but I don't see that happening at a customers request.

Finally got around to calling Delta today and the agent I spoke to said that there are no records of the downgrade and she can't see why any of this happened, she did call another department that she said would be able to look into this but they didn't offer any feedback that was useful either so more head scratching than anything else. I did go ahead and write a note to DL explaining the situation and asking for clarification/insight into what may have happened to my reservation last week and why I was downgraded on multiple flights at once.

I book through Concur and have never had that issue.

Multiple people at my company had the issue, and I read about it on a few other Delta-related sites. When reported to Delta, all they see is that someone/something rejected the upgrade or seat assignment.

I reported it to our travel people, and evidently it was a glitch due to some sort of setting that assigns seats (or tries to). When the upgrade goes through from Delta, it kicks it back to the originator (Concur in this case). The originator tries to assign a seat but can't do it due to violating policy or something to do with this setting, and then either rejects the upgrade entirely or rejects the Delta-assigned seat assignment.

I think our Concur administrators fixed the setting, as it appears to have stopped happening.

My reaction to the "no records of the downgrade" is to suspect that someone is trying to cover his/her tracks, but I suspect that someone higher in the organization or a good IT person can untangle the electronic record. I'd continue to pres and escalate if necessary. It's sounding more suspicious......

I've had bad things happen when I've somehow been upgraded before the ticket has been issued.

Quick update on this, finally got a response from Delta this afternoon for the note I sent. It was for the most part boiler plate with some minor tweaks to the message relevant to my situation and an offer for 9k skypesos for the inconvenience, I don't think whoever read my compliant quite understood what my situation was so I am starting to feel like I may not get very far with Delta on this one but I'll send a response back anyway.

O would call CS number, not the DM line, but the CS number. They have much more power to find out what happened/offer amends then anyone else at DL. Also emails can be misunderstood, while with call you know what is being said.