This has happened twice in the last few minutes. I post a comment, and decide I need to change it or add something and nothing happens after I open the edit window.
This happened once before and someone posted a work around, but at my age, my memory has left the building...
Are ya workin with a mobile device? I find th ability to edit comes an goes, on my Android device, much to my (multiple, extremely graphic expletives deleted!!!) chagrin.
A quick fix is a page refresh. If there is a bug in the Javascripts, that might be the cause. Posting a comment potentially exposes the bug and prevents editing after. A page refresh will sometimes fix this. F5 or better CTRL+F5.
For those that are inclined. If this happens on a PC, you can hit the F12 key to see the Dev Tools. Click the "console" tab and ensure "errors" are on.
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