Validation error submitting Dev ID signed application containing 3.1.2

Cannot pass online validation from Xcode of an app using latest ObjectiveDropboxOfficial signed with Developer ID credentials. Validation error message is:
**An error occurred during validation**
Couldn't find platform family in info.plist CFBundleSupportedPlatforms or Mach-O LC_VERSION_MIN for ObjectiveDropboxOfficial

version 3.1.2 info.plist contains a CFBundleSupportedPlatforms array item with 1 entry "MacOSX". I believe this key is either in error or being improperly validated. Apple seems to be phasing out the "MacOSX" nomenclature (it doesn't survive on their web site for example) and instead is using "macOS" or "MacOS". Why was this CFBundleSupportedPlatforms item added to Dropbox's framework? Is it an error? Was it tested vs. Apple's application validation checks?