LinkedIn connection marked unsafe

From time to time my LinkedIn connection gets marked as unsafe: no green lock next to the URL.

First, I believed this was a browser issue, but after I switched to another browser, the warning did not disappear (for now, my browsers are Opera and Chrome).

First, connection is always safe, but once I enter job search section and start scrawling through job offers, every now and then, although not often, the safe connection status turns into unsafe. Any one has an idea of what may cause such change?

Thanks for your attention.

The enclosed images further illustrate my question.

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