Unfortunately I can not share the full code (hundreds of lines of code), but this part is very isolated model wise. The issue is only with this constraint. If I remove it, I get exactly the same result with some of my other ampl codes.
I tried using
con_en_neutrality2 = constraint!(w, con_en_neutrality1, 1 => Pgen[v.i] - v.pg for v in data.cp_gen)
as neutrality constraint is single constraint, but I am receiving error:
LoadError: MethodError: objects of type Int64 are not callable
Maybe you forgot to use an operator such as *, ^, %, / etc. ?