Very interesting. By 'Horten HO', I assume that you mean the Ho IVb sailplane? (AFAIK, none of the other Horten gliders recovered by the Allies remained airworthy).
As for Robert Kronfeld, he was still in uniform in Sept 1945. S/Ldr Kronfeld was a member of Professor GTR Hill's Tailless Advisory Committee (and may have visited Bonn to help interview the Horten brothers after the war). Which poses the question: When exactly did Robert Kronfeld leave the RAF to become General Aircraft's Chief Test Pilot?
BTW, another member of the committee was K.G. Wilkinson, FRAeS. It was Kenneth Wilkinson who wrote the Oct 1945 RAE tech report 'The Horten Tailless Aircraft'. I mention Wilkinson because, it seems, that most of the test flying of the Ho IVb occurred at Farnborough. It was also there, of course, that the Ho IV was displayed statically for the Enemy Aircraft Exhibition in November 1945.
Sorry, I don't know the dates of the flight tests. According to John Christopher, test-flying of the Ho IVb continued until 1948. By that point, Kronfeld was definitely General Aircraft's CTP. Mind you, in The Race for Hitler's X-Planes Christopher also refers to "a conventional Bv 155B glider"! So, pinch of salt ...