@Hksp 

Is this on  specific device or multiple devices?

try rebooting the router and the device. Also check and adjust the firewall settings. 

  @ArcherC8 thank you!

I've tried reboot, then reset, then hw reset, then change the configuration, with no luck. It didn't work for iPad, and pc, and android phone.

it should not have so many issues, and even the internet literature (which I should have read before buying)  doesn't give me confidence.

I'll return it and I'll stay with the old ac1900 a bit longer, no issues in years...

  @Hksp 

by chance are you using a VPN as that can be the issue.