Now first to say nothing has changed ~ 7800DXL setup with static IP's for the wired PC and the wireless laptop & wireless printer in question.
Until today I used to be able to print fine from the laptop whilst it was VPN connected to my company systems...............but today it kept dropping the ability to print, initially I thought there was an wireless card issue in the laptop and rebooted it. That seemed to 'fix' it as was fine again for about an hour, it just kept failing to print. In frustration I disconnected the VPN and voila I could print again.
So what gives......................it was AOK before Xmas and now misbehaves with (so far) a reproducible oddity
Sounds more like a VPN issue than a Billion configuration router issue at your home.
Corporate VPN clients are usually set to "Tunnel All Traffic" i.e. send all traffic to the corporate network ... you can set them up for "Split Tunnel" i.e. send all corporate traffic to the corporate network and offload all internet traffic to the local connection, but this is often frowned upon due to security considerations.
So the VPN administrator could have updated the security policy OR there might be a routing conflict on the network where your local network address is also being advertised on the remote network and the VPN is routing it tot he corporate rather than offloading it locally.
Depending on the make / model / functionality of your printer ... I would recommend either direct connection with a USB cable or using a cloud print service such as google print service or Epson do a remote print service, some even offer an email to print service where you sent an email to your printer and it will print. Problem with the remote print / could solutions is that if you are printing something large it can be slow as you have to send it to the cloud first.
Right I sussed this one out, though why it played up in the first place was to me still strange!
I checked the printer Network settings in its browser GUI and it was picking up the correct static IP but its own settings were still showing it was set to 'receive' the IP via DHCP.
So I checked my old settings noted from when it was being used with the old Netgear, and made the changes to Manual IP and WINS entry but FWIW the WINS has reverted to Auto but IP field is still populated.
