Reason for this is that PhotoShop by default opens processed files in Camera RAW if a XMP sidecar file is present
There is two ways to solve this.
1. Change PhotoShop settings
Go to Photoshop>Preferences>Camera Raw
Change Jpeg and Tiff Handling settings from Automatically open options to Disable option
2. Change Capture One settings
By having XMP settings to full sync, Capture One will always create XMP files.
If you do not use metadata exchange over XMP sync then turn this off. Alt, set it to loan only.