Can't connect in LAN

I have a weird behaviour.

I have a Shadowsocks-Server running for almost 2 years now. It runs on a Raspberry Pi that also has Pihole and Unbound installed.

I use the Shadowsocks app to connect to this server and everything was working fine until just now. I can still connect to the server when I am outside of my LAN, but when I am connected to the LAN (with Wifi) the connection no longer works. It says: Failed to detect internet connection: Unable to resolve host "": No address associated with hostname

I am absolutely sure that this still worked a few days ago, as I often have the Shadowsocks connection turned on on my phone and when I come home, it just continued to work seamlessly.

But today I keep getting the error message whenever I try to connect. When I disable Wifi, I can perfectly connect with the mobile data.

I defined Remote DNS with the IP address of the Pihole (, but somehow it seems it can’t connect to it when I’m in the LAN.

How can I troubleshoot this?