The initial installation was 13, upgraded to 14 and then ultimately 15.
The error showed up after Softaculous had finished it's end of the upgrade and when visiting the website admin afterward in the final steps.
The error still occurred when the user_external was replaced manually through a file upload (all files in the module deleted and reseated). Since the info.xml file did not change in the new file upload, the error still occurred after the manual file upload.
This is more an issue with Nextcloud rather than Softaculous.
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