When playing on singleplayer, everything works as intended. On servers, none of the effects show up.

Same here, The fireflies do show up, but none of the "donation" customizations.

Try updating to the latest version

This actually helped. Altho I was on the latest update. but installing a new one did help. so thanks!

Same problem on 1.12.2 latest version, no config, don't work on server but work in single player. Someone can help me?