Updated the firmware successfully. Powered off the router, Mio TV and ONT. Powered on the ONT, followed by the router and lastly the Mio TV. After waiting for the Mio TV to fully load up, I am happy to say that it is now working again at Port 4.
I then connect my switch to port 1 (previously on port 2) and it's working as well.
Lan 1, 2 and 3 are all working now.
I do not have Mio Voice, so I can't test whether Lan 3 works for it.
Quite happy with this beta firmware, though I have not tested the Smart Connect yet as I prefer to assign my devices to the individual channels manually to get its maximum speed.