All of this raises more and more questions. The inconsistencies with the official version that you mentioned do cast doubt on its credibility. However, The Insider was able to identify two people "in blue sweaters" from the concert hall, they are not related to the secret services.
It should also be kept in mind that conspiracy thinking is extremely widespread in Russia and is part of its political culture. Versions based on conspiracy will only multiply in the absence of verified facts. This makes it easier for the Kremlin to cover up the evidence and the true organizers and perpetrators of the terrorist attack.