Blue Card & Citizenship: 6-Month Stays Abroad Each Year

Good afternoon,
on behalf of your description I would like to answer your questions in the following way:
When you plan to stay not longer than 6 months because of employment reasons out of Germany it cannot effect your right to ask for the german citizenship. The time is one reason, but in addition it depends on further circumstances, like having a flat still in Germany and paying rent.
I know, that sometimes authorities interpret rules in a different way. But we have standards depending on the law and it can't be, that sometimes authorities try to change it in their one way. If something like that will happen, when you ask in 2027 for the german citizenship and Einbürgerungsbehörde which is responsible for your application will refuse, you have the right to take the case to the court.
As long as you have your permanent address in Germany paying taxes, rent and so on here and you plan for the future no longer stay outside, it is not a problem. As you have written, your working practice will stop in 2027, it means, that this practice is only short-term and not for the next years.
There won't be a negative impact on your Blue Card. As you have written, you can stay for 12 months out of Germany without risk.
To avoid problems with your actual stay or in future, it might be a good idea, to get in touch with your "Ausländerbehörde". So you are able to get a better assessment and can avoid problems for the future.
The 12-month-period starts the day leaving Germany and ends when coming back.

I hope, that I was able to answer all your questions. Please, don't hesitate and ask a further one in case of not having completely understood my explanations.

Kind regards,
Ch. Schmauch (Lawyer)