Sadly the solution is to buy a router from the competitors next time. There are many right now with a decent ipv6 firewall configuration.

Is there a tplink product with a firewall configuration that allows the user to open a ipv6 port at firewall? I think there is not a single model with such feature. It's a shame, tplink devices...

@Kevin_Z Did you have manually configured the QoS download and upload speeds to match the ones delivered by your ISP? I have another tplink model (Archer A20) and it only works at full upload speeds...