In his interrogation TICOM I-15 (available in the TICOM folder) he shares some interesting information on the Soviet 5-figure code:
Q. What ciphers above division did you work on?
A. A five figure book which was re-encoded on a one-time pad.
Q. Did you have any success with this?
A. In the Finnish campaign the book was captured and the Russians used the one time pads over again. Because of this we had considerable success. Recently the Russians used the pads correctly, and only very few messages were read, these through re-encodements. Hollerith machines were used in attempts to break this cipher.
This makes Schubert the 10th person who explicitly mentions German success with Soviet high level codes in postwar interrogations.