Synchronised Blockstates
Setting up modded multiplayer servers can be quite challenging.
When you have multiple interconnected servers with different mod collections, it's common for blocks to mismatch across different servers, leading to visual issues like this:

This situation is clearly not ideal, so this mod addresses the problem by synchronizing all block states from the server to the client side when a player connects, allowing the client to properly display the world content.
Here's how the same world looks with synchronized block states enabled:

Important note: if the client doesn't receive block state information from the server, it will fall back to using vanilla game states.
This mod is still under active development (and has a rather unusual internal structure for specific reasons), but it should function correctly at the current time.