This just started recently and I can't attribute it to any plugin changes as far as I can remember.
It seems like I can edit newer posts, but not old posts (before I upgraded from legacy WP.) Again, this just started - I was able to edit old posts a couple weeks ago (I upgraded months ago.)
When I update the post and hit the "Update" button, it reverts to the previous unmodified version and gives me the error: "There is an autosave of this post that is more recent than the version below. View the autosave." When I click on "View the autosave" it shows me the correct, modified version of the post, but when I click on "Restore," it just gives me that error again and goes back to the old version.
It's like it's saving the correct version as autosave but won't let me revert to it. This is driving me nuts!