Cmsplugin-filer migration issue: How do plugins in CKEditor work?

Hi folks,

last Monday I dared to make the big migration from cmsplugin-filer in our websites to djangocms-file. At first glance it seemed to have worked out, but in the meantime my colleagues noticed that many linked media files like PDFs have disappeared. Only plugins in CKEditor fields seem to be affected, and the plugins were actually not really deleted, but they appear in the structure board under the the TextPlugin with a lock as usually, but not in the HTML code of the TextPlugin. One example of an HTML snippet where there was a file linked:

HTML before migration:

<p>26.08.2021: <cms-plugin alt="Datei - Bühne frei für die Königsklasse " 
id="394952" render-plugin="true" title="Datei - Bühne frei für die Königsklasse">
<span class="file"> 
<a href="/media/filer_public/32/1b/321be434-bd63-42c0-a117-4195c83162df/20210826_pressemitteilung_25_internationale_passivhaustagung_vor_ort_und_online.pdf"> 
<img alt="Icon" src="/static/filer/icons/file_32x32.png" style="border: 0px" />
B&uuml;hne frei f&uuml;r die K&ouml;nigsklasse 
<span class="filesize">
(1,4&nbsp;MB)</span></a> </span> </cms-plugin></p>

HTML after migration:

<p>26.08.2021:</p>

For the migration I used my own fork of David Bertrand’s migration app based on an undocumented Github gist, see also

So now I wonder what exactly happened and if I should restore the backup and if I can fix the migration. Probably it has to do with the plugin ids in the HTML code that changed after the migration.

Or is there any chance to fix the migrated fatabase at least semi-automatically. It would already help to at least identify all pages where FilePlugins are in TextPlugins

In the past we have migrated these manually.