Daniel here, VPNs are great...seriously you should use one, I do on all my devices.
Are VPNs supported by OWLR?
As it currently stands (07/12/2017), when discovering your cameras, VPNs are not officially supported by OWLR because of the way our app binds to the camera's ports.
Quickfix / workaround:
I personally use a VPN on my Android phone. The way I get around the issue of discovering and setting up cameras is by turning my VPN off, setting up all my cameras, and then turning my VPN back on! After your cameras are setup, you can use the app normally whilst keeping safe with your VPN.
This means you still have to setup port forwarding/UPnP, as you cannot use the VPN to access your local network from outside.
Note: I've only tested this on my phone, as the other devices in the office do not have VPN setup on them; so this isn't a guaranteed fix.
I still need help:
If you still need help, please get in touch with us using the in-app feedback button or email us here at support [at] owlr.com. We are more than happy to help!