The reasons for the cancellation was not clear.

In the pastI have bought tickets, they were cancelled a few days later. This turned out due to payment issues.

I personally had trouble buying tickets for a friend in Russia ( S7 Russia domestic flight), so what I ended up doing what asking my friend in Russia to pay with his credit and I would reimburse. S7 has issues accepting American and Swiss credit cards - much to my annoyance. This was largely fixed earlier this year with the world cup