I cannot put my finger on what triggers this, but for the past few days, I have had numerous occasions where mid-edit I notice that the Publish Changes is grey and not blue. This means I cannot save my edit and I have to exit and repeat the edit, which is very frustrating. Sometimes it happens even in a very simple edit. This edit shows what I was trying to do -- just add a few words. But the first time I attempted it, when I went to Publish Changes, it was greyed and I had to abort and repeat. The second time it worked normally.
I can't see any common factor in the kind of editing I was doing. But it's something that has changed within the last week. I don't recall encountering this before. I delayed reporting it because I was trying to work out what triggered it, but I gave up when I had it occur on the simple edit above.