Have you been warned not to use extended attributes because they aren’t supported beyond macOS? But they are: here are details of file systems and Cloud services.
iCloud Drive
Hectic with SIP problems in High Sierra, the Meltdown and Spectre vulnerabilities, then iCloud Drive’s strange stripping of extended attributes.
Don’t use iCloud Drive to copy docs between Sierra and High Sierra, as they may well lose metadata in the process. Bug or feature?
A strange problem with backups that start, but fail to complete successfully, apparently because of duplicate filenames. T2M2 to the rescue, bringing some important lessons.
The Eclectic Light Company 