I have an update:
Our Events page, which is set up like a gallery block, isn’t pulling in any “items” to display on the page. Across the website we have other pages that function in a similar manner (/blog or /take-action) which have not been affected (see comparison screenshot called collection comparison).
We have determined that it isn’t a template issue because we can pull in data from other parts of the site and display it on that page (as shown by the attached screenshot called template test) - pulling in the blog data onto the events template page.
We also set up a testing site and that was able to pull through items into the data feed with no issues.
We can also see that our /sitemap.xml url shows that Squarespace still associates the existing events under that collection, so the elements are there, they are just not being pulled through to the page.
The core issue seems to be that the CMS is not outputting the items array in the json endpoint for that particular gallery collection ie - https://www.curecancer.com.au/events?format=json-pretty (also shown through the collection comparison screenshot).
Any ideas on how we could get the endpoint to list the items array on our page?