Auto Weight 2D has a bad limitation.
If you look at the image below. The top joint chain is good to use with AutoWeight2D, the bottom one however will not work.
The joints need to not overlap in order for AutoWeight2D to calculate properly. Joint1 needs come before Joint2 in space.
The second joint chain will error because joint1 isn't the first thing on the line that the joints collectively make.
Some of the facial setups have a curve around the top eyelid.
If the curve even subtly bends underneath the rest of the curve, the joints generated for AutoWeight2D will not work. The highlighted curve below will work.