From Longman Dictionary of Contemporary Englishfall between two stoolsfall between two stoolsBritish EnglishCHOOSE to be neither one type of thing nor another, or be unable to choose between two ways of doing something → fall
Examples from the Corpus
fall between two stools• Overall, the study seems to fall between two stools.• That was a bad time for her because she fell between two stools in a way. 