The gif stream is pretty badly modded IMO. Someone over there keeps rejecting gifs that seem perfectly fine. It’s happened to me to and others; we talked about it recently right here in the Imgflip stream.
imgflip.com/gif/55759g
I still submit gifs to that stream every now and then, but it’s one of my less-used streams. Worth noting you can also submit gifs to the My_Custom_Templates
imgflip.com/m/My_Custom_Templates or NewTemplates
imgflip.com/m/NewTemplates streams where the moderation isn’t as uptight.