I am unable to get the URL that was previously used to add the album as it is not available/accessible anywhere. However, adding an album via new link that conforms to the url requirements, works okay. So, it is only an issue with some albums already added.
I recall changing album permissions sometime in the past from Public to ‘Limited, anyone with link’ – maybe this is the reason?
In any case, I re-added an album and Shashin retained the Photo IDs – which is great as I don’t have to readd each and every photo link to my old posts. So what I have to do is just re-add the albums, though I have about 15-20 of them broken.