Is there a security contact for flathub.org?

Is there a security contact for the contents of the flathub.org repository?

Assuming, something is wrong with a flatpak package, who can be contacted, and how?

I assume this is a issue specific to one application and resolving it with their developer is not possible?

In this case, you could send an e-mail to the admins by writing to admins@flathub.org.