I'll either save my gifs off of tumblr or save them through my phone (since I have a video to gif converter on it) and then upload them through giphy, I have all of the ones I've uploaded saved to my favourites so I can just grab the link to them instead of having to reupload them.(Pokecommunity hates tenor for some reason :( )
The two sites I've had a lot of issues with are tenor and tumblr, which sucks cause they're sites with a large collection of gifs. tumblr does this thing where it converts gifs uploaded to gif videos, which causes problems when trying to upload to other sites, and I've had trouble linking them directly from tumblr/tenor to... a lot of things.
Downloading them, making sure they don't upload as videos, and then linking them to here through giphy is probably the best thing I can recommend, it's what I've started doing.