Vienna, as a good neighbor, Franz had always closely monitored the civil war in Russia, and with the intelligence he had gathered, he knew that the Tsarist Government was about to concede.
To ensure domestic stability, Alexander II had been holding back from launching an attack, resulting in the rebel army gaining strength like a snowball rolling downhill, now threatening the rule of the Tsarist Government.
At this point, any shrewd monarch would choose to maintain their own rule first. Alexander II had to end the war before he could clean up internally and use political means to dissolve the rebellion.
Even a cornered dog will jump over a wall, and without ending the war first, those parasites colluding with the Kingdom of Prussia could probably not even safeguard St. Petersburg.
To confuse these people, Alexander II had already made a few scapegoats, which made it appear as though the issue had passed.