Private DNS says "Connected without internet"

Hi,

Recently, some users reported to me that Android devices using Private DNS show an error message "Connected without internet". But if you switch to another DNS server (example: Google DNS,..), Android no longer shows the error.

Device: Samsung note 9 (android 10), Pixel 3 (android 1)

With Samsung device, tried turning off internet connection check but still get error https://docs.samsungknox.com/admin/fundamentals/kbas/kba-1202-how-to-disable-the-internet-connectivity-check/

I have no way to debug more information, hope NextDNS dev will find a way to fix it. Thanks!