Your connection is not private on WordPress
Why it happens on WordPress
A WordPress site half-migrated to HTTPS serves the page over TLS but loads images, scripts or the login form over http://, and the mixed content trips the warning on some pages only.
The fix on WordPress
Set both WordPress Address and Site Address to the https:// form, run a search-replace on http:// asset URLs in the database, then flush every cache layer.
Is Your connection is not private happening on your domain?
Running the check from outside your device separates a real certificate problem from a local clock or network issue in one step.
Free, no signup. Runs from outside your network, which is the only way to tell a server fault from a local one.
If that didn't fix it
WordPress has its own failure mode, but Your connection is not private has a wider set of causes that apply everywhere. The most common one overall is: the certificate expired (net::err_cert_date_invalid).
All causes and fixes for Your connection is not private