TLDR: Delete any items without templates from your site’s content tree.
Recently when working with Sitecore Pages and my local docker-ized XM Cloud development environment, I ran into an error using the Pages editor. It had been working the previous week so I was stumped. My only clue was this error in the console: ApolloError: Object or reference not sent to instance of an object.
After scouring the documentation and re-doing my local setup, I was at a loss. Turns out, the solution was simple but (as of yet) undocumented, and probably the result of a recent update to Pages. Scouring the CM logs led me to the issue: items with no template.
Before signing off for the weekend, I had built a new component for this project. I pushed in all the code and serialization changes to my branch and opened a pull request for the team to review. When I came back to work on Monday, I swapped back to the development branch before spinning up my containers again.
Swapping branches and re-running serialization removed all the templates and renderings for my new component. However, it did not remove the test items I had created when developing the component, specifically the datasource items in the content tree. These items now had no template. Clicking them in content editor caused an error. And, it turns out, it was also causing the ApolloError in Pages.
To remove them, I had to use the Sitecore dbbrowser tool, at /sitecore/admin/dbbrowser.aspx. Once I did this, Pages was able to connect to my local environment again without issue.
Things move fast in the world of SaaS products like XM Cloud and Pages. This issue may be fixed next week, or it may hang around for a while. Regardless, it’s best to clean up any content items without a template in your local environments if you swap branches as you work on your project.