Why did German U- Boats attack neutral ships?

Some attacks were mistaken identity.

Some attacks were because the ships were sailing in an Allied Convoy.

Some attacks were because the ships were armed and Germany considered them as auxiliary warships.

Some attacks were because the British were beleived to be flying neutral flags on their ships to trick the U-Boats.

Some attacks were because the neutral was in Allied waters and the U-Boat Captain felt the ship was trading with the allies.