had a strange experience with not being upgraded on a couple of flights last week....let me know if any of you have come across something like this before....

the flights were bos-dtw-las booked in 'k' class & 3 days later returning on las-bos booked in 't' class....

i was 2nd on the upgrade list from bos-dtw, with only 1 seat left in first class....the person above me got upgraded so the system worked as it should....no complaints here....

i was again 2nd on the upgrade list from dtw-las with 5 seats remaining in first class....i was in comfort+ in seat 12c but just before boarding the upgrade went through & i was moved to 3a....while boarding i scanned my phone & a slip came out with my new seat assignment which had now moved me back to 14e....still in comfort+ but a middle seat now as compared to the aisle i had picked during booking....i pointed this out to the agent at the gate & she asked me to wait while she looked at what happened....she could see that the upgrade went through but couldn't explain what happened after that....after making a couple of calls & playing around with the system, she managed to get me an aisle seat in 10d in comfort+ but couldn't move me back to first since all seats were full now....she kept saying i was upgraded in error & that never should have happened but her explanation didn't make sense....i was 2 out of 20 on the upgrade list with 5 seats remaining so there shouldn't have been any error with the upgrade going through....

on my return leg i was 1 out of 12 on the upgrade list with 2 seats remaining....the upgrade didn't go though at the time of boarding but the app still showed 2 seats available....i thought it might be an error on the app & didn't say anything but the guy who was 2nd on the upgrade list pointed this out to the agent....she said all seats in first class were taken so she wasn't sure why the app was still showing 2 seats available....i sat down on my 11c comfort+ seat while the guy who was 2nd on the list sat down on his 10c comfort+ seat....the 2 seats in first remained unoccupied....when the boarding doors closed & the 2 first class seats were still empty, the 10c guy once again brought this up with the flight supervisor & questioned why the upgrade didn't go though....she said there is nothing she can do once the doors are closed & he would have to take this up with delta after they land....

what do you guys think????should i complain to delta or just let it go????i have no proof for what happened on the dtw-las leg but for the las-bos return leg i did take a snapshot of the app showing me as 1 out of 12 on the upgrade list with 2 seats remaining....the same 2 that presumably remained unoccupied....