This is unusual behaviour and not something we've come across before. Its a generic answer, but have you run First Aid on your drive using Disk Utility. Maybe there are some permissions which have been messed up. The other option is to delete Focused and re-install.
This is still Objective-C but will work alongside Swift until we get around to doing a Swift version. We have not had many requests for a Swift version which is why its not got to the top of the list yet.
If you can email [email protected] with details of your original purchase I'll get a discount code over to you for Particle Designer 2.0.