> insufficient gas buffers during the uptick of the economy after Corona

this is true

> Russia closing part of its huge gas supply to Europe

this isn't, afaik. Russia doesn't sell on spot market, they prefer long term futures contracts, on which they reliably deliver. They delivered on their 2021 commitments a bit earlier, hence they closed off the valves

Basically, the gas supplies were low during summer, but the spot prices were significantly above long term average, so energy companies delayed their purchases, hoping the price will come back down soon. It didn't, reserves dried up, and everybody was forced to buy at the same time

The gas prices spike has also other causes, like gas-powered electricity plants replacing or partly replacing nuclear facilities like Fessenheim in France. Gas-powered electricity plants are flourishing everywhere in the world, including China to diversify from coal, obviously at some point the available offer is not going to be enough.

Some businesses have a choice whether to use gas or electricity for example for heating. High prices of one caused them to switch too. I agree that effects on gas demand were secondary relative to energy, nevertheless my point stands that it is not unusual, and also we can’t count on gas when wind and solar farms are quiet.