Iframe freezes entire editor

I am trying to embed an appointment URL in an iframe to put it on a WordPress website. Oddly enough, when I go to edit the page using the Gutenberg editor, pages with the iframe freeze. I can still edit via Classic mode, but not Gutenberg. I have also posted this in a the company’s forum on Facebook and on Reddit, but I thought I would ask here as well. Has anyone else had problems with an iframe crashing the editor before? For what it’s worth, when I edit the page(s) in Classic mode, save, and then view them in another browser, the pages are fine and render correctly. I have tried this in two separate browser, Vivaldi and Edge, and it happens in both. Thanks in advance for any insites or help you can give.

Here’s my code (URL removed for privacy reasons):

<!– wp:html –>

<iframe src=”https://example.com&#8221; title=”Make an Appointment” width=”100%” height=”800px” frameborder=”0″>

</iframe>

<!– /wp:html –>