I'm having the same issue. the iframe content appears in edit mode, but not in the live mode. Ironically, I have 20 other pages using the same iframe that are working correctly!
Edit mode: https://krill-elephant-awdd.squarespace.com/barricades-signs
Live site: https://www.amosmetz.com/barricades-and-signs
I confirmed the https was consistent. Any other insight on how to get this iframe to render correctly?