It may be that the author of the template deleted their account / the underlying template. To check, go to the templates directory and see if it is still listed.
If it’s a purchased template, I suggest you reach out to Bubble support directly since you should still have some level of access, even if the underlying account/base template was deleted.
But if it is a free template, it may just be a bug that Bubble still shows it as a selectable option when it shouldn’t be there.