As with many popular productivity applications* Case Sensitive file systems are NOT SUPPORTED with FL Studio and Image-Line plugins. Case sensitive disk formatting is known to cause unpredictable behaviour and errors loading and saving projects.
When formatting a HDD for use with FL Studio and Image-Line plugins on macOS, choose:
Avoid the following case sensitive disk formatting options:
First, open Disk Utility. The easy way is to type "Disk Utility" in Spotlight and push the return key.
To open it manually...
In Disk Utility, select the main partition. Usually this is called "Macintosh HD".
Then click the Info button in the toolbar. This will open a window that has a list of entries, among which "Is case-sensitive" if in fact the disk is so.
Image-LIne Support Team
* Case Sensitive file systems are not supported by Adobe Products, ProTools and Steam for example.