Cannot Save a Page With an Unordered List

Site URL: https://www.berwynumc.org/facilities

I have a page where I am trying to do something as simple as create an unordered list.  I have used the wysiwyg editor and tried a code block and both only fail to save once I try to add the unordered list.  I am a proficient programmer in html, css, and javascript so I know it is not my simple ul and li tags in the code.

I can make the changes but when I save I get the following error.  Squarespace dm on twitter was less than helpful so I am reaching out here.  

To summarize: 

Steps to Reproduce:

• Enter a text box and click the unordered list icon to start a list
• Add all list items, exit edit mode.
• Highlight Done and click save.  

Expected behavior:  Add an under list in either the wysiwyg editor or in a code block, the list content render and save the page.

Actual Behavior: Receive an error that the page could not be saved and to refresh to try again. (see picture attached)

On a related note, I get the same error when trying to edit our main page that has unordered lists on it.