tiktok “no internet connection error”

i’ve been using tiktok in Hong Kong with a Hong Kong SIM card and VPN for a long time. when I was in mainland china, tiktok couldn’t load so i just thought it was due to stricter restrictions there. but now i only see “no internet connection” every time i open the app in HK, even when i’m connected to a VPN and using wifi. anyone know why this is and how to solve it?