Hi, just in case someone runs into that problem:
I wanted to add the Animation Starter Pack into a project. As I already had loaded this some time before into other projects, so it already exists in the VaultCache.
When doing the Add To Project, the Launcher crashed with some array index out of bounds error:
Other content worked, so it was only related to the AnimStarterPack. The Delete Local Content option of the Launcher also immediately resulted in the same crash.
So I decided to delete the content in the configured Vault Cache Location directly - fortunately, the content packs are just directories and simple to identify.
Deleting the directory AnimStarterPack48 in E:\Programs\Epic Games\Launcher\VaultCache and restarting the Launcher now forced a new download of the identical content into the Cache - and it worked again.