144h visa exemption

Hi there, we are German citizens on a flight from Bangkok - Shanghai- Seoul - Kunming - Bangkok. We would like to have 4 stopover nights at Shanghai and apply for the 144 h free exemption.
We do have confirmed tickets to a third country (South Korea) with confirmed seats, as German citizens we are visa-free in South Korea and Thailand. We do not leave Shanghai and stay in a hotel.
Are there any problems to be expected?