The following are the problems we are currently confirming.
We apologize for any inconvenience caused...
- Glitch where the art book can be viewed even if the DLC has not been purchased.
(Resolved but some users may still have artbooks in their local files.
For those who have not resolved the issue,
Uninstall->Reinstall this game from the Steam client should resolve the issue).
- Bug where DLC cannot be purchased even though it has not been purchased yet.
(We are currently investigating, please wait a while as we are in contact with Steam support...)