Turing TypeErrror Issue

I tried your suggested version of build_field, but now this generates the error:

type DataType has no field mutable

Stacktrace:
  [1] getproperty
    @ ./Base.jl:37 [inlined]
  [2] adjoint
    @ ~/.julia/packages/Zygote/zowrf/src/lib/lib.jl:281 [inlined]
  [3] _pullback
    @ ~/.julia/packages/ZygoteRules/AIbCs/src/adjoint.jl:65 [inlined]
# keeps going for a bit

But the switch to Zygote does appear to have addressed the other issue.

Also, are any of the interpolation packages compatible with Zygote for automatic differentiation?