Upon inspecting the App Store Connect website queries, I see that the API call to appClipDomainCacheStatus returns with a 500 error code: { "errors": [{ "status": "500", "code": "UNEXPECTED_ERROR", "title": "An unexpected error occurred.", "detail": "An unexpected error occurred on the server side. If this issue continues, contact us at https://developer.apple.com/contact/." }] } It really seems like a problem on Apple’s side.

I may have had an epiphany tonight: of course they're using FontLab (or Glyphs or FontForge), which is a tool specialized in making interpolatable, variable-width, vector-based… fonts.

I tried, and variations with MainActor.run{}, but the error still shows. Please see my other answer below.