The rejection states:
The key LSMinimumSystemVersion in the Info.plist file has the value '$minimumSystemVersion', which is invalid. This string indicates the minimum version of macOS required for this application to run and must be of the form n.n.n where n is a number. For more information, see the Information Property List Key Reference.
But the key's not even present in my Info.plist, nor is the string '$minimumSystemVersion'