No https unless refresh browser

Hi there. My sites are https secure unless I clear the browser cache. Upon the first page load, I get a mixed insecure content error as follows:

Mixed Content: The page at ‘https://sanjuanpuertorico.com/’ was loaded over HTTPS, but requested an insecure image ‘https://ads.scorecardresearch.com/p?c1=9&c2=13554685&c3=2&rn=1491970182&cs_xi=e54191e9-8d29-04f0-8811-8136df06ff67’. This content should also be served over HTTPS.

When viewing the page source HTML code, this link does NOT appear.
After refreshing the page in the browser, it then renders fully secure.

Have you heard of this? Any advice?