Assalamu alaikum, According to the Hanafi ulema there are no mistakes in Hanafi madhab - and according to the scholars of each madhab there are no mistakes in their madhabs. But in reality there could be and only Allah knows. For example are crabs halaal or haraam. Hanafis say haraam but everyone else says halaal. One of the groups is correct and the other incorrect. According to each they are correct but according to Allah there is only one correct answer. As long as we followed knowledgeable scholars Allah will not take us to task for following mujtahids and nor will the mujtahids be taken to task if they were sincere. There are hadith regarding this - for example it says more or less if a mujtahid makes correct ijtihad he gets two rewards (for ijtihad and being correct) and if a mujtahid makes wrong ijtihad he gets one reward (for making ijtihad) (but no sin for being wrong).