Noble Title Inheritance

Sims 4 Royalty and Legacy, my queen promised her noble title to her first-born biological son, and then the trait disappeared. Now it says that she can not promise the throne to him because he is the same level or a higher level, but he is a respected regent, which should be the rank right below her. It is really annoying because now her career task to "Promise Noble Title Inheritance to Family Member" can never be accomplished unless I promise it to his siblings, and it shows up every day now. I am also very worried that if she dies and he does not automatically inherit the throne, another noble may surpass him.