I recently switched to Snap VDSL, and took advantage of getting a Fritz.Box at a good price. Overall it's working well other than the following issue I'm having trouble solving.

I have a Western Digital Mybook Live NAS plugged into one of the Fritz's Ethernet ports. In the Mybook Live, I've given the device a friendly name, and usually I can access its web UI from a browser, and map drives letters in Windows, using this friendly name.

This all works fine with the Fritz.Box for a while, but eventually, if I attempt to visit the UI for the drive in my browser, or access any of the drive letters I have mapped in Windows, they cannot be found. Rebooting the Fritz.Box restores everything to normal again for a little while, then the issue repeats.

When things get into this state, I can visit the web UI of the Mybook Live by entering its IP address, so I know the device hasn't lost contact with the router. It's also showing up fine in the Fritz.Box's UI. I've assigned it a static IP, not really knowing what else to try, but that's made no difference.

Is there some configuration issue I've overlooked here that would be causing this?

Obviously the Mybook is the hub of all our media, so having it not integrating with the router properly is a big issue, and if I can't resolve this I'll need to revert to the VDSL modem I was using before.

Would appreciate any suggestions, thanks.