Dynamic link doesn't work with 2020

I can't render compositions from AE (17.0.6)  in Media Encoder (16.1.3).

- If I send comp directly to ME it doesn't show up.

- Load comp via file explorer in ME, progress bar works some time, then says "Project could not be opened" (or similar, translated from german)

- I have a project X, which doesn't connect to ME. I create a new empty project Y in AE with a new comp Z and send this comp to ME - works. Now i import project X into project Y and try to render comp Z again with ME - fails. So the simple action of only importing a project for which rendering with ME failed seems to break rendering for previous working projects / comps.

- checked all the firewall settings described in other threads on this issue.

- CC19 works.