> Does the hidden service log a client connection (either introduction or rendezvous) at the same time?
> If you turn on info or debug level logging on your client or hidden service, your logs might give you more information.
The earlier logs (which I stupidly deleted), would say about SOCKS errors, but it has now changed to saying it's an invalid onion address. The onion address and private key are definitely correct, and it works when Tor is first loaded. Give it 10 minutes, and it will stop working.
Try in your own client if there are other sections of the log you want.