Edit for clarification: I’m mostly asking about any issues with one kingdom ruling over Saxons, Pomeranians, Prussians, and any other german culture, like how the Austrians had a hard time with their Bohemian subjects but on a lesser scale.
Can you please elaborate on what exactly you're asking for?
I'm assuming you are targetting internal disorder or challenges within the Kingdom of Prussia because of its non-Prussian, German-speaking population.
Alternatively, your question could also be interpreted in a much broader fashion to encompass conflict potential between the Kingdom of Prussia and its non-Prussian (but German) neighbor states. In that case, are you asking about the time before the German unification of 1871 or after?
Thank you!