This sounds like a problem with the computer itself. Sadly, I don’t fully understand any of the Linux distributions or how they work. I can tell it’s your computer doing this considering it does the exact same thing with both Prism and Minecraft launchers, but just in case I’m wrong, you could try other free launchers and see if they have the exact same result. If you need to, you might need to consult someone who specializes in Linux systems to fully figure out the problem as well as fix it.
Have you tried testing it in other chunks to see if it’s just that chunk that the hopper doesn’t work properly in? If it doesn’t work anywhere else where you tried, then it could be a problem with the realm. Another way to check is to copy the seed of said realm, create a world with said seed, find the exact coordinates where your hopper is (if possible), build the contraption, and test it for the same results in that world.
By the way, I’m not someone who works for Mojang Studios or Microsoft. Just a fellow gamer with a somewhat decent understanding of computers.
Well, it’s still in the experimental stage, so hopefully this gets ironed out before or during the official release.