When building for iOS with XCode generator, MACOSX_PACKAGE_LOCATION prepends '../' to the path given
MACOSX_PACKAGE_LOCATION property behaves as documented only for macOS. For iOS, however, if the location is set to something other than 'Resources' then it will be prepended with '../' effectively placing the files outside of the bundle. The 'Resources' value seems to have a special meaning on iOS and the files are actually placed in the bundle root. But if use 'Resources/AnotherFolder', it gets prepended with '../' as well.
I've also found this message in the mailing list describing the same problem: https://cmake.org/pipermail/cmake/2016-August/064125.html