Surprising runtime behaviour with objective types about nlsolversbase.jl HOT 2 OPEN

mutable struct OnceDifferentiable{F, DF, FDF, TF, TDF, TX} <: AbstractObjective
    f::F # objective
    df::DF # (partial) derivative of objective
    fdf::FDF # objective and (partial) derivative of objective
    F::TF # cache for f output
    DF::TDF # cache for df output
    x_f::TX # x used to evaluate f (stored in F)
    x_df::TX # x used to evaluate df (stored in DF)
    f_calls::Vector{Int}
    df_calls::Vector{Int}
end

 0.000015 seconds (3 allocations: 224 bytes)
  0.000005 seconds (1 allocation: 160 bytes)
  0.000001 seconds (3 allocations: 960 bytes)
  0.000000 seconds (1 allocation: 896 bytes)
  0.000002 seconds (4 allocations: 8.016 KiB)
  0.000001 seconds (2 allocations: 7.953 KiB)
  0.000011 seconds (5 allocations: 78.281 KiB)
  0.000011 seconds (3 allocations: 78.219 KiB)
  0.000178 seconds (5 allocations: 781.406 KiB)
  0.000110 seconds (3 allocations: 781.344 KiB)

  305.021 ns (3 allocations: 224 bytes)
  53.191 ns (1 allocation: 160 bytes)
  326.941 ns (3 allocations: 960 bytes)
  86.506 ns (1 allocation: 896 bytes)
  850.000 ns (3 allocations: 8.00 KiB)
  596.154 ns (1 allocation: 7.94 KiB)
  6.100 μs (4 allocations: 78.27 KiB)
  4.520 μs (2 allocations: 78.20 KiB)
  45.800 μs (4 allocations: 781.39 KiB)
  47.400 μs (2 allocations: 781.33 KiB)