Samsung Galaxy S7 Edge user here. I haven't solved the problem though I did notice one thing in particular that may be of help to some people. When sent, for GIFs below 1MB, the GIF remains at its normal speed. Anything larger than 1MB is sped up when sent.
I'm lucky enough where, by default, my GIF options automatically tell me how large the GIF is before I send it (in the top right hand corner of the message box underneath the GIF, after selecting the GIF). So if you have this option, you at least have the ability to send GIFs smaller than 1MB without issue.