I am not 100% up on the recent stuff, and I have not read the entire thread, but Russia was blowing up pipelines to Georgia back in 2006. It may be that the Russian were trying to freeze the German out of the war. Russians, to my understanding have been running under the assumption that Western countries would cave to public pressure to not get involved. After watching Trump getting pushed cutting and running in Syria and Afghanistan (not to mention their invasions & asssassinations in the former republics), they may have expected to have a half hearted set of sanctions imposed by the West, bulldoze Ukraine and be back to business. Cutting off the flow of gas and making the Germans freeze for the winter, in the minds of the Russians, might prevent Germany from giving full support to sending arm to Ukraine. No one can send Leopard tanks to Ukraine without the Germans giving the thumbs up. Germany is central to NATO and miserable and cold Germans could split the West. Russia has always had a habit of misreading the West. After watching four years of Nato being undermined, I could see Putin betting that turning off the gas to European civilians would weaken resolve. He has been using a similar strategy of destroying civilian infrastructure on the ground in Ukraine.