Advice on 144hr TWOV in Shanghai.

I need to know if we would qualify for the 144hr TWOV in Shanghai
We arrive in Shanghai as follows JNB-HKG-PVG on Cathay Pacific
We depart on a Costa Cruise leaving Shanghai with first port of call in Naha/Okinawa (Japan) within the 144hr time limit
We both have full british passports
On the face of it all looks good for us meeting the rules but complication is that the cruise also docks in Sanya (China) later on in the cruise
Have read in other sites that if you visit China again as part of the departure it is considered double transit and this thus violates the rules of the 144hr TWOV
Does anyone have advice on this