This is Russia's Winter War. They're figuring out what is wrong with their military to fix the issues.

Russia sent their best. Just all the so-celebrated paratroopers of superhero-style reputation in Russia, now suffering heavy losses in their brand new BDM-4 aluminium death traps. The elite tank units with their so hyped T-90s and other new tanks (sans fuel). The pilots battle-trained bombing Syria for almost a decade, where they also tested all sorts of new weapons (they officially proclaimed over 160 of their new weapon systems of all kinds have been battle tested there). The supposedly world's best air defense, now finally in "proper" Russian hands after failing in so many other conflics where the said failures were being blamed on the non-Russian operators. All sorts of special forces, including these of the interior ministry in large numbers. The Chechen loyalists groomed for 20 years as a new generation literally, the raising of whom costed simply ridicalous amounts of money (these guys for most part grew up rich and not only for Russian standards). High ranks with supposed hard-earned experience from Chechnya and elsewhere. They even have fought the Ukrainians before.

It's not a bunch of 2020 annual conscripts, it's what Russia has spent so many years organizing with all their costly military reforms and investments over decades, and just recently also many months preparing directly (it was only launched when they decided they were completely ready). It was supposed to be finally their true show of power, but now they're just literally stuck in the mud, the very definition of quagmire.