Board Thread:LotR Mod Technical Support/@comment-79.155.155.180-20180109202218/@comment-27219153-20180109204309

It's just the way horses are in vanilla minecraft. The horse position is calculated server side while the player position is calculated client side.

Here is a simplistic sequence of events:

You hold 'w' to go forward on your horse.

You move forward a few blocks.

The server needs to load/generate new chunks and stops moving your horse so it can do this.

The server updates entities and tile entities.

The server calculates your horse position again and you move forward several blocks.

Repeat this cycle indefinitely.