[com.battlelancer.seriesguide] Login to SeriesGuide Cloud not possible

Affected app
Name: SeriesGuide
Package id: com.battlelancer.seriesguide

Describe the bug
When trying to login to the SeriesGuide Cloud (a service, where you can sync your lists of movies and series) the following error message appears: Fehler bei der Google-Anmeldung (API_NOT_CONNECTED) (should be something like error logging in to google...)

To Reproduce
Steps to reproduce the behavior:

1. Go to 'more' (bottom right)
2. Click on 'SeriesGuide Cloud Login' (second from top)
3. Error should already appear. If not, click 'Login'

Expected behavior
You should be asked to enter your account credentials for SeriesGuid Cloud.

Screenshots

System
Device: Pixel 1 (sailfish)
Android Version: 10
Custom ROM: LineageOS 17.1 with microg

microG
microG Core version: 0.2.17.204714
microG Self-Check results: All ticked

Additional context
SeriesGuide is the first App I installed after setting up the custom ROM.
I also installed the extension with id=com.battlelancer.seriesguide.x which gives some paid features. This worked fine and was also recognized.
If have not installed any other apps then theesse two and the pre-installed ones.

Start by reproducing the failure through More > SeriesGuide Cloud Login on the listed Pixel 1, Android 10, LineageOS 17.1 with microG setup, and inspect the Google sign-in path associated with the API_NOT_CONNECTED message. Done means the login flow no longer fails at that point and allows SeriesGuide Cloud credentials to be entered.