Additional chat-related features and issues within Microsoft Teams for business
I had a similar issue on our Teams, whereby selecting a Gif used to load frame by frame and very unreliably, basically Gif options were next to unusable when searching for them. Optional Connected Experiences were enabled already, I went back disabled that and enabled it again and Gif's loaded instantly so for those that found this thread through a similar search, hopefully this helps to solve your "Gif not loading or Gif loading extremely slow" issues.