I looked at the 2019 GBD weights but found "Moderate wasting without edema - Asymptomatic" has weight of zero with uncertainty limits [0; 0]. This makes little sense as this corresponds a a state of perfect health which would not warrant it being labelled a "disease" and we know ther is some mortality associated with moderate wasting.

I think we would not want to use that. I think we could start from, "Severe wasting (without edema" which is weighted:

        w = 0.128 [0.082; 0.183]

and use the low uncertainty limit (i.e. w = 0.082) as the disability weight. We usually want to have uncertainty limits for this. We could use something like:

        lower = 0.082 - (0.128 - 0.082) = 0.036
        upper = 0.082 + (0.183 - 0.128) = 0.137

giving:

        w = 0.082 [0.036; 0.137]

This is a rough and ready approach to the problem. Others here may have a better idea of how to do this. You shoiuld check that I have read an copied the table of disabiloity weights correctly and if my arithmetic is sound.

I hope this is of some use.