Template part has been deleted or is unavailable error

@michaelapproved Whew! Thank you, thank you so very much.

I also just started to see this error. My use case might be different but might trip somebody else up, so here’s my fix to my issue.

Cause: I had renamed my child theme and only then did the issue crop up. My theme uses templates exported from the previously named theme. I then noticed that in the templates the theme name for the header template part is specified.

<!-- wp:template-part {"slug":"header","theme":"my-theme-child","tagName":"header"} /-->

Fix: All I had to do was edit the template(s) so that the theme name matched.