V13 backoffice - RTE - iFrame - frozen browser

I have this issue where, in the backoffice on a content node, there is an RTE that has some text and an iFrame of an embedded YouTube video. A content editor goes to this node, and as she scrolls down and gets the RTE in view on the browser, the browser freezes and gets the “(Not Responding)” text in the browser tab. When there is no YouTube iFrame in the RTE, it works fine, she can scroll the page with no browser crash.

This happens every time to her, on multiple browsers, different computers, logging into different user profiles created for her. Whenever I try it, there is no browser crash.

Has anyone come across something like this before / have any suggestions for resolving this? Thanks.