YT error: “This video is restricted. Try signing in with a G Suite account”

This happens frequently to my wife on her mobile phone even when on the same WiFi network as me, but doesn't on my phone. We're both not using YouTube app, but NewPipe, Firefox Klar and Firefox Fennec.

She tried logging into YouTube on desktop browser and turning Restricted mode on/off, but it didn't help.

The issue seems to occur with non-mainstream media covering (Serbian) oppositional topics.