As both voluntary and involuntary attacks are resolved under the same Combat Phase, to satisfy the two markers the Russian unit would have to attack twice which isn't allowed under 10.3.4.

Am I missing something?

To confirm, the defending German player chooses which hex applies for Terrain Effects purposes i.e. you could ignore the "no beneficial terrain combat modifiers" aspect of the Counterblow hex and use the Terrain in the other Target Hex instead?

Rule 10.6.1 indeed seems to imply that to me!