It sounds like you might have a corrupted ArtRage preferences file.
To delete the ArtRage preferences file, first make sure ArtRage isn’t running – you might have to force-quit ArtRage from the dock menu.
From your MacOS file explorer menu:
1. Click on the Go Menu.
2. Hold down the Option key - This adds a Library item to the menu. Select that.
3. Open Application Support / Ambient Design / ArtRage
The ArtRage6.PRS is in there.
Move the ArtRage6.prs file to the trash.
When you start ArtRage it will start up with the default settings.