According to Franks et al. in
Casualties of the German Air Service a Leutnant Eckstein and his pilot, Leutnant Richard Dietrich of FA23, were made POW on April 22, 1917. I always assumed this was the Wuerttemberger Otto Eckstein, but I see a later entry in the same work which lists Otto Eckstein as being wounded on January 25, 1918 with FA264. Were there two Ecksteins?