Links on page behaving very strangly. Can’t understand what’s happening.

Good morning to you all,

I link to a page that has two things, a ? back to the last page link ? that works fine and underneath is a shortcode that opens an URL for an external website in an iframe. I have a different page for each URL.
The shortcodes are :
US Airways : https://www.usairways.com
[iframe src=”https://www.usairways.com/” height=”480″ width=”100%” scrolling=”yes”]
Delta Airlines : https://www.delta.com
[iframe src=”https://www.delta.com/” height=”480″ width=”100%” scrolling=”yes”]
They are identical.
I am completely baffled. Both URLs are correct as they open fine in any browser on their own. On my WP page the first works however the second one and several others, do not. Even if I empty the cache but no difference. Anyone got an idea.