From Longman Dictionary of Contemporary Englishlabour under a delusion/misconception/misapprehension etclabour under a delusion/misconception/misapprehension etcWRONG/INCORRECTto believe something that is not true She had laboured under the misconception that Bella liked her. → labour
Examples from the Corpus
labour under a delusion/misconception/misapprehension etc• Well, dear Rex was either lying or labouring under a misapprehension. 