Get online support
I found a similar issue in the thread below, maybe it's worth trying another port as they did in the end eg one of the WAN/LAN ports?
https://community.tp-link.com/en/business/forum/topic/539964?sortDir=ASC&page=2
More info, not sure i understand the solution though
https://community.tp-link.com/en/business/forum/topic/87766
Do i need to set an internet VLAN on the ER707 such as they have done in the below photo?
@thehvacdude . ER707 does not use VLAN. That is done by VR1600.
With VR1600 in normal mode, connect a computer to each LAN port to check each one works.
You can leave the DNS addresses empty initially. They will be set from TPG when the ER707 connects.
Have you specified which port is the WAN port?
Go to Settings > Wired Networks > Internet. Tick the box corresponding to the WAN port you want.
You may need to contact TP-Link support.