ckeditor/convert redactor, redactor anchor, redactor custom styles to ckeditor issue with lost content in matrix fields

[remoflury]

Description

I have a craft installation, where we wanted to update to the newest version. Within this update, we already tried to get rid of the deprecated redactor plugin, in favor of the ckeditor. On ckeditor/convert the migration of all fields and content takes place succesfully.
However, inside some of our fields, no content is migrated: The content seems to be lost.
This is strange, as this occurs inconsistent and without an error. Inside of some matrix fields, some content is lost, but other isn't. Moreover, the error only occurs in matrix fields or supertables.

Steps to reproduce

1. Have a Craft V4.5.6.1 installation with the plugins Redactor, Redactor Anchor and Redactor Custom Styles
2. Install CKeditor
3. migrate with ckeditor/convert
4. Test all entries, if the migration was successful and if content has been lost

Additional info

• Craft version: V4.5.6.1 -> V4.12.5
• PHP version: 8.3.12
• Database driver & version: MariaDB 10+
• Plugins & versions: Redactor 3.1.0, Redactor Anchor 1.5.0, Redactor Custom Styles 4.0.3, Supertable 3.0.15

[mikejpeters]

I think I've run into something similar, and running the Craft CLI resave command before running the creditor migrations seemed to help. In Craft 5 I used craft resave/all but in Craft 4 I think you'd have to run a more specific command like craft resave/entries and/or craft resave/matrix-blocks.

I've also found that things seem more likely to mess up if you deploy multiple migrations at once to a production site, so it's better to deploy them one at a time.