Chrome web browser "Your connection is not private" error?

The Chrome message "Your connection is not private" means there is some issue with the website SSL certificate. It is often caused by an old SSL certificate, SSL certificate issues (wrong subdomain, etc.) anti-virus program issues, etc. The most common SSL errors are displayed in Chrome as follows:
NET::ERR_CERT_COMMON_NAME_INVALID (server-side fault)
NET::ERR_CERT_AUTHORITY_INVALID (invalid certificate authority?)
NET::ERR_CERT_DATE_INVALID (check your PC date/time)
The SSL errors most commonly occur for one of the following reasons:
- The certificate is not up to date
- The connection between the browser and the website may not be secure
- The certificate is not issued by a trusted organization (as determined by your browser or anti-virus program)

You can try the following steps to fix the issue when it happens:

1. Clear browser cache: "Settings > Show advanced settings > Clear browsing data", or, even reset the browser if you want (you shouldn't have to do this): "Settings > Show advanced settings > Reset settings > Reset".

2. Make sure your PC date is correct - if it is some date in the future it may cause SSL certificate expired errors.

3. Turn off ad-blocking extensions in your browser - some ad blockers may cause issues with parts of websites not showing, turn them off temporarily (or completely for that website) to test.

4. Turn off third-party anti-virus for a minute to test - they can sometimes cause SSL certificate issues.
- Avast Free Antivirus: Settings > Active Protection > Web Shield > Customize > untick "Enable HTTPS scanning"
- Bitdefender Antivirus: Settings > Privacy Control > Antiphishing tab > turn off "Scan SSL"

5. Proceed to site anyway. In Chrome, you can simply click on the "Advanced" link in the lower left corner of that message and "Proceed to the site" (you should only do this if you know what the error details mean, i.e. look at what is wrong with the security certificate). To see the security certificate in Chrome, try: F12 > Security tab.

6. Check for malware. Run Malwarebytes and AdwCleaner, to make sure there is no offending malware or browser extensions that may be causing the issue.

Note: It is also possible to set Chrome to ignore SSL certificate errors by adding the " --ignore-certificate-errors" switch to its shortcut. This is not recommended, however, as it leaves you vulnerable to attacks.