I have recently updated my blocks to json markup, they are working correctly EXCEPT when I change an ACF field value that changes the visuals/content of a block. E.g. Colour selector as an ACF field which changes the background colour of the block. These break in the backend with “This block has encountered an error and cannot be previewed.” Displays correctly on frontend and when the backend is refreshed.
I have tested with renderTemplate instead of renderCallback and this didn’t fix the issue. Also backtracked to registering in PHP and worked this had no issue.