Hello katarinajan,
Thank you for using Apple Support Communities. Sounds like you're not able to see a Shared Album anymore. Allow us to share some information with you. The following resource here explains what happens if a Shared Album is deleted: How to use Shared Albums in Photos on your iPhone, iPad, and Mac - Apple Support
When you delete a shared album, it's automatically removed from all of your devices and the devices of your subscribers. If you turned on Public Website, the shared album is removed from the web, too. Deleting a shared album permanently deletes all of its photos. Before continuing, make sure that you save any photos that you want to keep.
Shared albums are also not automatically backed up. The following resource explains that you must save photos that are in your Shared Album to your library if you wish to save them: If Shared Albums aren't working - Apple Support
If you were not the creator of the Shared Album, please ask the creator to send you an invite. We hope this information is useful. Thank you for using Apple Support Communities. Take care.