I had missing meta files in a package, and reimporting did not regenerate them. And since packages are not created by me, I did not know what to do to get the meta files. So what to do? Solution: I did go to console and right clicked on the package. Then selected "open in explorer". In windows explorer I deleted the complete package. Then I reopened the project in Unity, and at package, I selected reimport all. Conclusion: This was unfortunately the only way to make unity know that I needed new meta files.