This is really obscure, but maybe it will help someone here.

With the open-sourcing of Lightning Web Components on May 29, 2019, I was really excited to dig in! From Christophe Coenraets
Salesforce’s blog post, I eagerly clicked the link to the LWC
 only to be met with an error in my browser.

The site was fine though. I saw other colleagues access it in the office. And I could ping it with a valid response
from the server. I noted that the LWC site used a .dev domain extension and immediately suspected
that I had messed up my local DNS configuration from previous local development. In a past life, I had done quite a
bit of local website development with vhosts and apache. Back then, .dev was a common domain extension
for testing sites locally. However, .dev is now available as a common TLD.

Anyhow, after some digging, I opened up terminal (I work on a Mac) and went through these steps:

  1. scutil --dns in terminal
  2. Looked for any resolvers like:
    resolver #8
    domain : dev
    nameserver[0] :
    flags : Request A records, Request AAAA records
    reach : 0x00030002 (Reachable,Local Address,Directly Reachable Address)
  3. cd /etc/resolver && ls

In that directory, I found a file named ‘dev’. All I had to do was delete that file and could then view the LWC site in my browser with no errors.