Just discovered something. Now, this is in regards to the 3 second glitch.
As I stated earlier, I switched to Wave from MS Edge. The entire box appeared and stayed visible. I was able to assign a reaction symbol as before. Of course, about a week later the 3 second glitch appeared.
A few minutes ago I hovered over the box to appear. I chose an icon, clicked on it and held for 3 seconds, released, then had the chosen icon appear in the post. I found out that you actually have to wait for 3 seconds before releasing or otherwise the same message will appear. Did it successfully for 5 or 6 times and this method seems to work each time.
Hope this is of some help to you and the others with the same frustrating problem.