Thanks for getting back to us, @Geoff Bex. Allow me to point you in the right direction, so you'll get the appropriate assistance you need in resolving your network drive issues in QuickBooks Desktop (QBDT).

Before anything else, I appreciate you performing the suggested troubleshooting options provided by my colleagues above. 

In some cases, undetected network drives can be caused by various technical factors such as network settings, firewalls, security configurations, or even hardware failures. That said, I recommend reaching out to a qualified IT professional to diagnose and resolve such matters. 

Moreover, you'll need to restore a backup of your company file so you can undo recent changes whenever you encounter problems in QBDT.

Please don't hesitate to drop by the Community if you have clarifications about managing your network drives in QBDT. I'm always here to assist you further. Keep safe!