The Soviets moved the capital from Petrograd to Moscow in March 1918, largely because of the vulnerability of Petrograd to German attack. Even before, some embassies had moved out to Vologda with Soviet assistance. Despite this, the cancel is still in use in April 1918 on the Weinert cover.
How long did it continue in use? Was a new office created in Moscow and did it have its own cancellation?
My November card is addressed from Station Vyiya on the Bogoslov railway to the Italian Embassy in Petrograd, where the Government and Diplomatic office handled it on 6 November 1917. My December card is addressed to the Swedish Mission (or Legation) from Sukhrinskoe in Perm guberniya and was handled by the Government and Diplomatic office on 10 December 1917. Howard Weinert's 1918 item is fully written up below: