Do Russia request another mobilization? On the number and failure of Russian troops in Ukraine

Recently, the Chief Intelligence Board of the Ministry of Defence of Ukraine announced that the Russians were preparing to announce and carry out another mobilization. They're expected to mobilize from 400,000 to 700,000 recruits. Interestingly, information has already appeared about a more circumstantial number of 420,000 people to power the ranks of the Armed Forces of the Russian Federation. The question so arises – why do Russia request specified an influx of fresh meat erstwhile it is so good?