I have an AGOL Scene that I am using iFrames to embed bookmarked locations into a website. About 50% of the time I am getting the following error:

The issue is fixed with a refresh of the page, but I would love to know if there is something else I can do to prevent the error from coming up.
The only modification I made was I changed the link to https in the embed for each bookmark in the AGOL scene.
Here is an example link in the site: Book of Fortresses
Thanks!