A standard new project is working as expected so I do recognise that it is something within our project setup that might be causing the issue but finding it is the hard part.
The challenge is it's a 5+ year old app.
I did a side by side comparison of all the build settings between a new app and our current one and all the settings matched bar one (Runtime hardening). I enabled this and no change in behaviour.
Looking through the build logs, I can't see any message about the outcome of CODE_SIGN_INJECT_BASE_ENTITLEMENTS.
Any help here would be greatly appreciated!