I had the same problem today. In my situation I had a different identifier in my original app than in the extension identifier "base". The extension has to have the same identifier as the original app plus something else. E.g:
Dummy App: com.company.dummy-app
Dummy App Extension: com.company.dummy-app.extensionName
After Xcode told me that, I changed my wrong names to look like above and then the problem occured.
The problem was, that I had "automatic manage signing" turned on but xcode didn't recognize that I changed the identifier.
Solution:
Just change the identifier again and chek if in "automatic manage signing" a new provisonig profile was created.
Deleting derived data may also helps.