GIFs not working for iOS recipients

This issue pops up frequently when I upload (as opposed to pasting links to) GIFs into a chat room.
Other Riot Android users see the GIFs and can play them.
iOS users, however, only get a blank space where the GIF should be. There's a way for these users to see the GIF in its full splendor but only if they long press and save it to their device and then look through their gallery app.

I'm an Android user and I don't have an iPhone at hand for more succinct testing, but this happens more often than not, so should be fairly easy to reproduce [tm].

We are using our own homeserver. The versions of server and clients are frequently updated, but may not be running at bleeding edge on everything. Multiple iOS users have experienced the "blanks" of the same GIF.