"Unable to open [object Object]:..." error

I was hoping to try out a few Library of Congress maps for a class this week, but I keep getting this error!

I suspect this is the same error as a bug reported for Courtauld Institute images?

Example 1 -

https://www.loc.gov/item/2012593214/

Manifest:

https://www.loc.gov/item/2012593214/manifest.json

Example 2 -

https://www.loc.gov/item/2021589948/

Manifest:

https://www.loc.gov/item/2021589948/manifest.json

However, this one works:

https://www.loc.gov/item/99446220/

Any thoughts?