IIRC that message is for when you’re in a captive portal. II also get it every once in a blue moon. Even when I’m at home, on my custom network, browsing the internet.
It happens when the check can’t reach the Arch Linux server for a ping. It can be disabled, although I am completely unsure how.
I installed Pi-Hole and there I observe pings to ping.manjaro.org, always a block of four pings, that are being blocked by pi-hole. I’d suppose that these things are correlated.
Did it for my network at home, so now it’s OK if something is wrong with the 'net. I’ll know before switching on my PC anyway, so that is kind of pointless. Now if there’s an error, its quite obvious where the problem lies.