That is the page I have had the issues with. But this happens with multiple access points and devices. I have had it happen using the app/phone browser and from my desktop. It isn't my connection, I don't believe, because I don't have other issues anywhere else, and this only started just a few weeks ago.
This started about 2 months ago when I was trying to start over from scratch, which also included changing the themes, etc. Somewhere in THAT process, the error messages started. They are internal messages coming from your side, but I cannot figure out why.
For a while I got the message on every tag that I tried to update, and it also happened while updating certain pages. I haven't noticed it happening to blog posts yet. But the one commonality is that it always happens when using EDIT but not QUICK EDIT, which is another thing that makes me hesitant to say that it's from my end.
Like I said before, it only happens periodically. And it hasn't happened in the past week, but I have also stopped changing tags right now, and when I do I just use the Quick Edit to do it unless I need to change the description.
One thing, this doesn't happen when ADDING a tag. It only seems to happen when using the EDIT periodically.
I know it isn't the browser cache because I've cleared that along with rebooting, and as I said, I've tried using multiple devices including my phone which also uses cellular data to connect.