It’s fixed!
Going by your suggestion, I looked on my dashboard and the only plugin that looked like it might have something to do with Facebook was Super Socializer which provides a Facebook button and other social buttons for people to share posts with.
I deactivated Super Socializer, then reactivated it…and that fixed the problem.
Thanks for the clue, Anders.
The reason my replies all have the same date is that previously when I first replied to commenters, I did not like having my responses being stacked at the bottom, so I deleted all my responses.
But after being unable to find a fix on my own, I retyped all my responses on the same day before posting in this forum because, as the adage says: A picture is worth a thousand words.
As for the “enable threaded (nested) comments” setting, it is and has always been activated.
