Bundles are locked in Zylpha when another user has them open, or the bundle is in the generation process. This is to avoid two users accessing the bundle at the same time, causing conflicts to any changes they make.
You can see when a bundle has been locked by the small padlock icon on the bundle row.
Or you'll receive a toast notification indicating the bundle is locked by another user.
If another user needs access to the bundle, you can unlock the bundle by exiting the bundle page, back to the homepage or bundle list. It may take a moment, but the bundle should unlock for the other user.
Note: The other user may need to refresh the page or wait for generation to finish.