Is a student of knowledge sinful if he favors an opinion based on its evidence, then abandons it to adopt another opinion in order to avoid disagreement and out of precaution for his faith? And is he obligated to act upon what he has favored when issuing a fatwa? What is the ruling if the opinions are equally balanced to him and he takes the more cautious one?

Acting with precaution in matters where there is a difference of opinion is a good thing and keeps a person away from sin, because it fulfills the saying of the Prophet, peace and blessings be upon him: "Whoever guards against doubtful matters has indeed cleared himself (in regard to) his religion and his honor." However, if the precaution contradicts a clear Sunnah (definition), then it should be abandoned at that point.

Shaykh al-Islam Ibn Taymiyyah said: "Precaution is good, as long as it does not lead its practitioner to contradict the Sunnah. But if it leads to that, then the precaution is to abandon precaution."

So, if you act with the most cautious approach for yourself, there is no harm in it. And if you issue a fatwa (definition) to people with it, explaining that it is the most cautious for the religion and the safest for one's conscience, then that is good.