We have reported this issue to Apple (FB7706647) and we are currently awaiting a response. Solution: Update to macOS 10.15.6 and CCC 5.1.20. Many folders on the destination volume will appear empty, and the volume will not be bootable.
If you're establishing a new backup of macOS 10.15.5 or later, CCC 5.1.17 (and earlier) will be unable to create a correctly-functioning APFS volume group. The chflags system call no longer works correctly on 10.15.5 with regard to setting the special 'firmlink' flag that establishes links between the System and Data volume group members.
Apple introduced a bug in 10.15.5 that prevents the creation of firmlinks
