Tom, I'm not following what exactly you're doing with the URLs. There should be no reason to do a right-click anywhere to insert a giphy image.
I was trying to post a gify I found on the gify site, not using the button. Like copy/paste an image without using the image button.
Then I tried to find the same image, using the button and went thru 15 pages and still didn't find it.
In the past, rt clicking an animated gif and pasting the gif into a reply worked (like one from pinterest) but now, it doesn't work.
Rt clicking a gify image from the gify site also does not work to paste into a reply.
Adding just the identifier string into the gify button search also does not work to find the specific gif.
You try to find the Godzilla roar gif using the button. (IU7KDfmmKCJXi) specifically.
Then, when you don't, add just any gif and replace the identifier string with the IU7KDfmmKCJXi string and it works.