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:
Spawn in a boat or boat w/ chest in a patch of water in any gamemode or spawn in a boat on land
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.
This is now resolved, if a mod would update it. I tested it in the latest stable version with both boats & chestboats and it works smoothly now. They also fall smoothly. If you would like you can double check it inside of your game, and once you do this can be marked as resolved.