Alipay's health code nucleic acid test has always been single-tube negative. Why is the mixed tube in WeChat still positive?

Information delay. Alipay's health code nucleic acid test has been negative for single tube, but it is still positive for mixed tube in WeChat because of the delay of information. In order to improve the efficiency of positive examination of mixed tubes and reduce the risk of cross-infection, when mixed tubes are positive, the positive testing institutions in our city will notify the list of mixed tube personnel to the data special class for a series of verification, which will take a long time.