I would be suspicious of a Russian pullout. They have already said nukes are on the table.
It is common in warfare to pull a unit (division) off the front line periodically and replace it with a unit sitting in reserve. I recall from when in Korea, our division would be taken off the line and the division in reserve would take over our sector. That was true for all branches except the artillery. Our mission would change from direct support of our division to general support of the incoming one.