iFrames blocked all of a sudden

Hello Community,

I just inherited an Intranet project based on the Yii2 Framework.
I’m completely new to Yii and I’m trying to understand why:

“iFrames are being blocked all of a sudden?”

I get this error message in the browser console:

scheduler.production.min.js:14 Uncaught DOMException: Blocked a frame with origin “https://www.marinetraffic.com” from accessing a cross-origin frame.

The iFrames have been working correctly for the last 6 months, then suddenly are being blocked.

I’ve tried adding the following to my .htaccess, with no luck:

Header append X-FRAME-OPTIONS ALLOW-FROM https://www.marinetraffic.com/

Any suggestions?