After some extensive testing, thanks to @Msql a bug with tab-complete not working on a bungeecord with ViaVersion and MultiLobby installed was fixed.

Now you can find new config option called "multilobby-priority" that will allow you to set priority of MultiLobby ServerConnect event that is used to balance players.

Note that value HIGHEST will fix Viaversion issue on bungee, but might potentionaly cause unpredicted behavior to other (bungee-side only) plugins that are using this event. So you might wanna set it to just HIGH or NORMAL depending on the plugin.