UCC28064A: When the 220V AC input is turned off, there is still a drive waveform

Dear Expert

Due to an abnormal supply of UCC28063, the customer is now switching to UCC28064A.4KW communication power supply, LLC uses TMS320F28032 as digital power supply.

At present, the customer debugging found that when the 220V AC input is turned off, there is still a drive waveform of about 2K frequency lasting about 200~500ms, which has a great hidden danger to the power safety of the customer. Could you please help to give some advice?

Red: drive waveform blue: large capacitance waveform;