You cannot attack or use items while you're in a boat while using the new touch controls. It only seems to affect crosshair controls, but not touch and classic. It is very hard to use items or weapons while in a boat because of this. I marked out the area where they're supposed to be. This bug report is different from MCPE-160396 since I mounted on a horse when I reported the bug, but as you can see the dismount button bug still persists too even in boats