Hey @weLees,
Please remember there is a process to request auto-connections. When creating a post, you should explain which interfaces you are requesting auto-connection, and the technical reason behind that request.
Still, I found there is a related post where you already provided explanation but the latest snap declaration is not matching the original request.
Also, by taking a look at the latest version, I see you are still using system-files for accesses we already mentioned other interfaces should be used instead. The system-files interface is typically used to provide read-only access to system configuration directories created by a non-snap version of an application now running from an equivalent snap which is not this case.
Did you try plugging system-observe and hardware-observe (or others) as suggested?
I recommend running snappy-debug while troubleshooting, it will recommend interfaces based on the behavior it observes in your snap.