How to remove extended attributes from all files in a folder on mac
To Remove All Extended Attributes On Many Files
To recursively remove extended attributes on all files in a directory,
combine the -c &quot;clear&quot; flag with the -r recursive flag:
xattr -rc /path/to/directory

Open Terminal.app and start typing xattr -rc  , include a trailing
space, and then then drag the file or folder to the Terminal.app
window and it will automatically add the full path with proper
escaping.


Source: Taken form cwd's answer to: How do I remove the “extended attributes” on a file in Mac OS X?