I recently added a new site collection to a SharePoint 2013 environment and attached a restored content database from a different environment (also 2013).
The process involved was:
backup SP database on original environment
restore database to new environment
add restored db as new content database in SP
create new site collection to use the new db
It all worked fine, with no issues occurring, but when I view the Site Contents in SP, the only libraries visible are the standard ones (Documents, Site Assets, Site Pages, etc) - none of the libraries that were part of the restored database appear. A count of AllDocs confirms that the documents are in the db - it's just there are no libraries showing.
I can confirm in the Site Collection List in SP Central Admin that the new site collection is pointing to the right db. I've also double checked this from PowerShell using: