Hey, thanks for your comment and stating your system and version information. You're using an older version of CSP, the current version is 1.8.5. Please consider updating to the latest version, it's free of charge and this issue seems to only orrur with earlier versions of Clip Studio Paint. If you're worried about losing your settings and brushes, create a backup of your system beforehand. All the settings are located in "[your home folder]/Library/Celsys", if you want a quick backup instead.
If your problem still persists even after updating, please consider contacting the official Clip Studio Support:
www.clipstudio.net/en/contactTheir support page states problems with importing brushes for version 1.7.1, maybe their solutions could help you out:
www.clipstudio.net/en/support