Sort:  

A quick update, I was later able to edit an older post. I don't exactly know how but according to what folks said on Discord servers, the problem was partly due to bugs in I think the Hive blockchain itself and/or at least just the Hive Blog application which rests on top of the blockchain. If I run into it again, I'll take your advice and try my active key. I also tried changing my node a few times but I don't think that changed it. But the good news is the problem is probably fixed now.

I have just edited an old post using only my posting key. I think your response to my last comment is right on the money. About a week ago I couldn't post anything at all on Peakd or Hive.blog. While I was investigating whether it was the PeakD/SteemPeak software or the hive blockchain it seemed to right itself.