[Steam in Flatpak Sandbox] Renpy based games not starting

[Gego/XAREN]

I am having problems with Renpy based games when running them from stream in a Flatpak enviorment, The error I get is:

undefined symbol: PyUnicodeUCS4_FromEncodedObject

The github discussion on the subject can be found here:
https://github.com/flathub/com.valvesoftware.Steam/issues/54

I am starting to suspect that the Steam client is doing something fishy when stating the games that make them behave this way.

Any ideas?
Much appreciated if the Linux client devs were to give some kind of feedback.
:-)