I'll bite, here's a little list of the top of my head.
They've had a failed invasion of Ukraine
Rampant corruption
Putin is getting old and frail
Russia has a struggling economy where "Fortress Russia" is starting to fall short
Drone strikes from Ukraine have been able to target major Russian cities.
There was a mini-coup attempt by one of Putin's closest allies where a standing army nearly made it to Moscow while shooting down multiple Russian military aircraft.
The linked article hypothesizes "a rump Russia reduced to the area bounded by St. Petersburg, Moscow and Nizhny Novgorod." Even given the country's struggles, I have a hard time imagining large chunks of Russia breaking away. My question is whether there is evidence to believe that kind of split has become a real possibility. Neither Putin nor his successor would allow it without a serious fight given the immense value of the natural resources and sea ports Russia would lose.
Imo, anyone who's going to try to break away from Russia, ahem Serbia, would wait until Russia's military collapses before they make any official announcements.
But plenty of Russian allies have secretly worked against Russia itself, won't be long before they're all doing it as overtly as Turkey's Erdogan.