ModelingToolkit can't find a variable its knows as an unkown

[branch171]

I have an InitializationProblem problem and for some unkown reason ModelingToolkit can't find a variable that it knows is an unkown.

Here is my list of unknowns produced after structural_simplify()

compressor1₊T_out(t)
compressor2₊T_out(t)
mixer₊h_out(t)
separator3₊inport₊T(t)
(separator3₊inport₊z(t))[1]
(separator3₊inport₊z(t))[2]
compressor3₊T_out(t)
separator4₊inport₊T(t)
separator4₊inport₊mdot(t)
ERROR: UndefVarError: separator3₊inport₊T not defined in ModelingToolkit

As you can see separator3₊inport₊T is in the model at least before I call:

iprob = ModelingToolkit.InitializationProblem(sys,0.0,merge(Dict(u0), Dict(para)))

Has any one see this type of behavior before.

[branch171]

This is related to @register_array_symbolic functions. If you have a @register_array_symbolic function and this has a variable to be solved, i.e. an unkown, then ModelingToolfit can't solve the equation. If I warp the vector returned function so its not used and return a scalar for the equation to be solved it works fine. The issue is I have high overhead as other equations us the same vector values so I am calling the function too many times.