I downloaded the Adobe Cleaner Tool and scrubbed InDesign from my computer. I tried clearing the Adobe font cache by deleting ALL instances of ' adobefnt*.lst'-files. I copied the font to the Common -> Adobe -> Font folder.

The font is obviously installed in the Windows Font folder, so I tried re-installing it. It's a bespoke font bought directly from the designers: The font is not in the Typekit or the Adobe cloud font library. Today I updated my Creative Cloud (Photoshop, Indesign, Illustrator, Premiere Pro) to the latest versions and found that in InDesign - and only in InDesign - one* of my installed fonts were listed as 'missing' when I tried to load the documents I had been working on previously. I hope the issue will get upvoted and fixed shortly!

I have the same issue! And I've only solved it - temporarily - by downgrading to v16.4.