Surprise

Today I finally managed to get my eCard to work as a citizen card ("Bürgerkarte") with more than just the federal tax online aplication ("Finanz Online").
I could - for the first time ever - access the federal pension plan application (PVA) as well.

It was not easy, and I really don't know what I did differently with the (I guess) 3rd approach, but it finally worked.
And now it seems to work stable, i.e. I could access the site and authenticate with my eCard a second time...

After only more than half a year of struggling.
Amazing.

Now that this is done, and now that I know my future pension ... it's time to retire :-)