plot_model bugs with functional submodels

[martin-gorner]

Repro Colab (10 lines of code) : https://colab.research.google.com/drive/1a36L_zVwmwyocsdLsasYjmnK8nyY6mny?usp=sharing

[martin-gorner]

This is a purely sequential model, containing purely sequential submodels, but the plot_model utility does not show the layer graph connected as it should (see repro colab)

[dhantule]

Hi @martin-gorner, thanks for reporting this.
I have reproduced this issue in this gist, we'll look into this and update you.