Hello Philip,
One thing you can do is to check if the data importer works in a blank new project.
If so also install your other marketplace modules in there, if it is still working then compare the userlibs between the two projects.
If it is not working create a ticket by mendix support it is a platform supported module so they should give assistance on it.
Hope this helps,
Good luck
PS: i also saw lately a userlib cleaner on linkedin did not had time yet to dive into it but it looked promising
https://www.linkedin.com/posts/mitchelmol_mxignitefeatureflashadventcalendar-mendixignite-activity-7268904159741984768-xMHA/
https://www.linkedin.com/feed/update/urn:li:activity:7280153298190446594/