If this is only happening on your iMac and you are running the same version of Studio One on your MacBook Pro, I would recommend removing your settings from your settings folder in Studio One. Here are instructions:
1. Go to Help>Open Settings folder.
2. Copy the contents of the folder over to a folder on your desktop.
3. Close S1 and delete the contents of the settings folder with the exception of the user.license file.
4. Open S1 and go to Studio One>Options (Preferences on a Mac) to reconfigure your settings.
5. Test to see if the problem is resolved. If it is not, please feel free to copy your settings files back over from the backup that you created in step 2.
If you need to reset your PRAM, here are some instructions:
https://support.apple.com/en-us/HT204063
If you continue to have an issue, you may want to submit a support ticket so that we can get some system information from you. You can submit a support ticket at my.presonus.com under the Support tab once logged in.