404 not found with nginx below it message. Is it okay or is it harm?

I just got that message on my desktop, and the wifi indicator had '?' sign on it. And then I restart my laptop, it's all gone.

What is that all about?? Is my laptop back to normal now?? Or do I need to do something more specific to solve this??

Sounds like you lost connection to either your router or your ISP.

But I still can accessed the internet like Youtube. That message hasn't show up anymore, but I really want to make sure it's harmless and not breaching the security of my system.