Is it permissible for a Mufti's fatwa to contradict a judge's ruling, such as in the case of divorcing a menstruating woman? And what if the questioner acts upon the Mufti's fatwa both before and after the judge's ruling?

It is permissible for the Mufti to issue a fatwa according to what he deems to be preponderant, even if it contradicts the judge's ruling. The judge must submit to the truth. This is supported by Ibn Mas'ud's fatwa, which differed from Abu Musa's fatwa regarding the inheritance of a sister's daughter with a sister, after which Abu Musa reverted to Ibn Mas'ud's fatwa. As for the questioner, it is preferable for him to act according to the opinion of the majority. He should also know that a judge's ruling resolves disputes between litigants, but it does not make lawful what is religiously forbidden. A Muslim should be scrupulous and adopt the opinion of the majority, which was held by the four Imams, and consider a divorce pronounced during menstruation to be an effective divorce.