And if you shoot an arrow when you're riding a Minecart, it will destroy it.
I think that Minecraft can't display FallingSand entities with a tag Time:1 , because It work with a FallingSand entitiy with Time:0 (when you place a sand block, it summons a FallingSand entity with a Time:0). And I think (but I'm not sure) that when you join a world with a FallingSand Entity, it will always turn it into a FallingSand with Time:1 .
I have this bug as well in 1.16.4
The workaround in the post worked for me but i'd love this to be fixed.