After some digging i figured out that it was only happening to vimeo videos.
Open themes\pinboard\scripts\fitvid.js
on line 49…
change:
“iframe[src^=”https://player.vimeo.com’%5D”,
to
“iframe[src^=//player.vimeo.com’]”,
There is a deeper issue. I’m not sure why the vimeo links are being generated without the ‘https:’, but this fix worked for me.