Blocks with no collision (eg tallgrass and torches) should not slow down iceboats. Yet they do. This isn't the case in Java edition, and in previous versions of Bedrock.
Items with no collision do not slow you down.
They do slow you down, some more than others.
Steps to reproduce:
1. Make a blue/packed ice strip
2. Put a block with no collision on the strip (such as redstone dust)
3. Ride a boat down the strip
When you get to the block, then you will slow down. After you get off it, then you speed up again.
Full list of blocks that do this:
-All types of buttons
-All types of torches
-All types of rails
-All types of signs
-All types of fencegates (open)
-All types of ferns (inc. nether sprouts)
-All types of coral fans
-All types of crops
-Both types of mushrooms
I assume it also affects flowers, but I didn't test those. I also attached a video with the ones I tested.
This needs to be fixed because there is no current way to spawnproof blue ice roads because of this bug.
PS: Carpets and pressure plates stop you completely, so I assume other blocks with very small collision boxes do this as well.