Sounds like some of the issues that you and others are experiencing may be due to the fact that it is Schedule Change Saturday --
This
should not be related; this occurred a few days ago, and I contacted Delta at the time. They had not responded and so I did some more research and wrote the article. Since the article Delta has contacted me and said 'that is the way it is supposed to be' you should not be able to see seats 'you cannot manage' and 'it's not a glitch.'
Their statements indicate an intent to do this. Again, they did this earlier this week; before a Saturday schedule change and they seem quite content in its result.