See attached jpeg which shows RR movement when different units are selected.
The left image shows RR movement for Sov. Cav Dorps in Daugava. It can move throughout the Riga area.
The right image shows RR movement for the Sov 17th Mech which is adjacent to Riga.
This occurs regardless of weather since earlier this area was clear and still had problem.
The restriction seems to be any unit in the area around Riga marked by the the Red dots can't use RR to move anywhere.
Units outside of this area can freely move into the Riga area using RR movement.
Germany and Russia are not at war.
In April 42 Germany declared war on Russia.
At that time the restriction disappeared and all Russian units in or out of Riga area could use RR there.

