When try to join the download stops at 65% and "Bat" error occurs.

Just a heads up, this is for version 1.21.111, which I couldn’t select in the “Affects version” section. My friend added a few addons to our Realm. Now whenever I try to download the addons and join, the download bar on the loading scree stops at about 65%. After a few minutes I get a message that the server could not be found with the error code "Bat". On the rare occasion that I do join the realm, several textures are missing or broken, and multiple mobs become invisible. Update: After reproducing the error page, the codeword it suggests I search on the help page appears to be random.