Fix a minor bug

Author: YingboMa

src/systems/nonlinear/nonlinearsystem.jl

@@ -77,7 +77,10 @@ function NonlinearSystem(eqs, states, ps;
         throw(ArgumentError("NonlinearSystem does not accept `continuous_events`, you provided $continuous_events"))
     name === nothing && throw(ArgumentError("The `name` keyword must be provided. Please consider using the `@named` macro"))
     # Move things over, but do not touch array expressions
-    eqs = [0 ~ scalarize(x.rhs) - scalarize(x.lhs) for x in eqs]
+    #
+    # # we cannot scalarize in the loop because `eqs` itself might require
+    # scalarization
+    eqs = [0 ~ x.rhs - x.lhs for x in scalarize(eqs)]
 
     if !(isempty(default_u0) && isempty(default_p))
         Base.depwarn("`default_u0` and `default_p` are deprecated. Use `defaults` instead.", :NonlinearSystem, force=true)