Tp-Link Touch P5 Router ONLY works when connected to another router
I'm experiencing a weird problem with my Tp-Link Touch P5 router that even Tp-link support could not resolve, so I hope someone here can enlighten me. When the router is connected to the modem (via Ethernet), I get a WAN Port Unplugged error and cannot connect to the internet. The problem is neither the cables nor the modem because I can access the Tp-Link's configuration on my computer, and I can also access the internet if I connect my computer directly to the modem. However, if I connect another router to the modem (in my case an old and slow Netgear) and connect that to the Tp-Link via Ethernet, same port, same cable, and still configured as a router, then the Tp-Link works perfectly. Moreover, every time the Tp-Link boots, the time and date resets to 1970, but eventually updates once connected to the internet via the Netgear. I had a similar problem with another Tp-Link Touch P5, but its WAN port did not work regardless of what it was connected to because of a power outage. I do not think the WAN port of the new router is damaged because then it should not work when connected to another router.
I don't want to keep using the old and slow Netgear as a workaround to get the Tp-Link to work, but that's the only solution I have right now. If anyone has experienced a similar problem and resolved it, of if there's a networking guru here who knows what's going on, please help!