Ferenc Nagy (The Struggle Behind the Iron Curtain, 1948 translation) claims that this occurred in Hungary (so not quite Eastern Germany, though Hungary was occupied by Germany from 1944 until "liberation" by the USSR):
The barbarism of the Soviet occupying forces can best be judged by the fact that many thousands of Hungarian men were raped or forced to unnatural excesses by Russian women soldiers. The Reds established a recreation camp near Kecskemét for more than thirty thousand sick and convalescent women members of the Soviet army and the police forces. From this camp, for instance, the Russian women banded together at night and swooped down on the surrounding hamlets, kidnapping the men and sometimes holding them captive for days. Often these abductions led to the peculiar girls hiding, not themselves, but their men in the forests and in haystacks to keep them from the disease-ridden Soviet women troops. The facts were first reported to the Swiss legation in Budapest; the results of its investigation were published by the Swiss Foreign Office in May, 1945, as a warning to the world.
Cecil Eby (Hungary at War, 1998, p. 24):
When they began shipping random Hungarians to the USSR as slave laborers, Sághy decided it was time to leave. He hopped a freight train moving south toward Szeged, but near Kecskemét he was caught and arrested. His warden was a Russian female soldier who forced him to have sex with her. Afterward she turned him loose, and he escaped in the darkness.
(On p. 21, n.9 states, "Interview with Gyula Sághy (February 23, 1989).")
Krisztián Ungváry (Battle for Budapest: One Hundred Days in World War II, 1998, 2003 translation, p. 290)
Four cases of men being raped by female soldiers are also known.
(Accompanying note states, "Interview with Szablya; communication by Vadász.")