Browser
ERR_BLOCKED_BY_CLIENT Something on your machine blocked the request
What it means
The browser, or an extension, or another local filter, stopped the request before it left your machine in the usual way. The site may be fine. Your client refused to fetch it.
Where you usually see it
Advertisement blockers, privacy extensions, corporate filters, and some "security" add-ons. It often appears on a single script or image, and sometimes on a whole page.
What to try first
Try a private window with extensions disabled, or another browser with no add-ons. If the page loads there, turn extensions back on one at a time in your usual browser until you find the one that blocked it. You can then allow that site, if you trust it.
When to stop
Disabling every extension permanently is a blunt fix. Do not disable a filter on a site you do not trust just to make an error badge go away.