For goodness sake, why does Xcode keep doing this?

I can offer some suggestions that might help in resolving or mitigating the issue:

Clean Derived Data: Try cleaning the derived data for your project. In Xcode, go to File > Workspace Settings, and then click on the arrow next to the Derived Data path to open it in Finder. Delete the contents of the folder.

Restart Devices: Restart your Mac, iPhone, and Xcode. Sometimes, issues can be resolved by restarting all the relevant devices.

Check Console Logs: Open the Console application on your Mac (/Applications/Utilities/Console.app) and check for any error messages related to Xcode or your app during the installation process.

Check Provisioning Profiles: Ensure that your provisioning profiles are up to date and properly configured. You can refresh them in Xcode under Preferences > Accounts > Apple IDs > View Details.

Check App Signing: Verify that your app is signed correctly. Check the signing settings in your Xcode project and make sure the signing identity and provisioning profile are valid.

Update Xcode: Ensure you are using the latest stable version of Xcode. If you're not already on Xcode 15.2, consider updating to see if the issue persists.

Diagnostic Reports: If the issue persists, you might find more detailed information in the macOS Diagnostic Reports. You can find them by going to Console.app > Reports > User Diagnostic Reports. Look for crash reports related to Xcode.

Thanks @BornP for answering and making some suggestions, more than any of the Apple folks have done.

Unfortunately none of these do anything to rectify the issue. Once again I'm unable to do anything, things were going fine one minute, then the next Xcode threw one of these episodes. I have 6 iPhones and its stopped working with all of them, that was several hours ago and since then just cannot install/run the app at all (same app as was working just before, no changed made).

I also have 3 Macs and have observed this on all 3 of them. The one thing they all have in common is they all have Xcode 15 on them. None of these issues started until I started using Xcode 15 beta, its been present in every Xcode 15 beta and every Xcode 15 release version, including 15.2.

I'm going to have to raise an official Apple support ticket, my MacBooks been out of action all day long because of this.

Must I really raise an official support ticket to get an answer to this?

You could try that, but (a) they probably won’t be able to reproduce it, and (b) if they do reproduce it, they’ll say “That looks like it might be a bug. Please report a bug. Thanks. Bye.”