The common problems investigators experience is of noncompliance which standard analyses, such as the intention-to-treat or as-treated analysis, casual effect. So in RCT with crossover treatment, if you specially look for noncompliance for example control participant receive the intervention and intervention participant receive the control in order to evaluate outcome non-responder. This way we can address the missing data, In addition Multiple imputation methods for treatment can address noncompliance and nonresponse.