Welcome to the forums! You're talking with other users here, not Verizon support. Which is exactly what you want, as Verizon doesn't officially support non-Verizon routers.
It should work fine. Verizon's network infrastructure currently allows two active DHCP leases for exactly this situation. You used to have to release the IP before unplugging the old router, but no more. You may find articles on the web that describe this old process, especially on sites that re-publish old articles in an attempt to generate ad revenue. You do not need to follow those steps, although they are not harmful.
Note that while their router's allow two DHCP leases, only one is allowed to pass traffic. The dual-lease support is only to make it easier to switch routers.
At this point, I suggest you verify the Ethernet link is good between the ONT and TP-Link. If the TP-Link has status lights, check them to see if a 1Gbps link is established. You should also be able to check link status from the TP-Link's dashboard. If you don't have a solid link, try a different cable.
If that still doesn't find the problem, there could be a DHCP lease issue. Verizon WAN leases are usually 120 minutes. Waiting 5 minutes is not long enough. You should be able to check the current lease renewal time in the G3100's dashboard. You can also try releasing it before swapping. I'd be surprised if that works, but it might.
I don't have a G3100, so I don't know the exact location of the WAN DHCP settings. In the G1100, it's on the "Broadband Connection" settings page. Look for something similar in the G3100