honestly I think there were a lot of issues around caching and cache-busting early on in the site to the point where we don't do it any more because then after an outage or planned upgrade people's browsers would have cached broken emojis every time and there was much consternation. This should be a surmountable problem, but if devs and power users aren't using the emoji picker much or are using it on desktops with fast connections...

I don't know of a workaround really that's client side but I'll look for one. Firefox mobile? (I'm guessing with any other browser you're SOL due to no extensions)

Edit: honestly not sure why this doesn't work, the images seem to come back with this header which should cache them for a week

cache-control: public, max-age=604800, immutable

maybe we have so many browsers are refusing to cache them all

2dit: also worth checking if you've configured it to clear cache every time you restart the browser or something, I've been known to do that kind of thing and forget