Try unpublishing and republishing the folio.
Today we had "Issue Unavailable" in the same sprint 20 branded viewer for the two different issues on the two different iPads - on one of them it was issue #0202 and on the other - issue #0203. That is why I decided to reinstall the app. And the reinstallation of the app fixed this issue on both iPads, so it looks like this message caused by somehow corrupted app data.
Bob, could you please ask developers how this issue could be fixed as we don't want our readers to face the same problem.
This bug was fixed in v21 (June 20) Release:
I'm still experiencing this issue. The unpublishing and republishing workaround does work, but the bug does not seem to be fixed.
Had same problem today on both iPads - 1st gen. and 2nd in v22 viewer. So the bug is still persist.