Telephony: No Telephone numbers enabled
And it seems all the call history was lost, now there's nothing to show in the Call List

However making / receiving calls are fine no problems
I also found this under the Overview section:
Your FRITZ!Box contains basic settings adjusted for your Internet service provider: Additional information.
Never seen this kind of message before. I tried to click the "Additional information", but the link doesn't work. I don't know what was changed / adjusted
Restarted the FRITZ!Box, and updated the firmware to the latest 6.04, still the same issues

Any thoughts?