There is an update for the custom fields. I have version 4.4.12 and want to update to version 5.8.3. It says the compatability is supposed to be 100%.
However, when I do the update, the data for the custom fields on all sites is gone. I looked if the data is still in the wp_postmeta table in the database and it is. So it seems the data is still there, but does not get found anymore when updating. This problem happens in two of my projects.
How can I fix this?