I am not optimistic we'll solve the GIF issue. The Xenforo expert I had look at it cannot replicate the issue (neither can I). It's not related to our style. It's not anything global (such as one of our add-on's or the Xenforo upgrade causing it). because only some of us are experiencing it. It is likely related to the browser version some are using (or possibly the settings your specific browser or browsers are set to). With so many variables (operating system/windows versions, device types, browser types, versions, and add-ons, etc.. it is very difficult to nail down.
The best advice I can give you is, try different browsers. If you use specific browsers, maybe try turning off blockers or other add on functions and see if you can fix it from that side. We will no doubt upgrade again before long and maybe this will be resolved with future Xenforo upgrades.