Boats and boats w/ a chest (All wood variants) lag whilst being pushed or moved. This happens when you are swimming, and you push the boat it has a very laggy animation. Also when a boat is falling, it also acts as it is lagging. I have a decently high spec PC and the games performs very smoothly, so I have provided a video attachment for further evidence, but here is how to reproduce it:
 

1. Spawn in a boat or boat w/ chest in a patch of water in any gamemode or spawn in a boat on land
2. Push the boat when it is on the water, by either swimming or flying, and it will not push smoothly or if boat is on land, break blocks underneath it, it will produce a rather laggy fall

This happens in both the main version of Minecraft: Bedrock Editon & the latest version of Minecraft Preview, this does not affect Minecraft: Java Edition, boats work smoothly in Java Edition.