I am "Unable to save" my survey as when I try share it publicly.

At the same time, when viewed publicly via the share link, the following message appears:

I am the admin of the account and all share permissions set in the organisation's security settings allow public submissions.
We have created a publicly shared survey previously without any issues, in fact, it still works currently. Even when merely trying to duplicate that survey, public sharing doesn't work.
Any suggestions are welcome!