Technically, NAT Boost reduces CPU usage.

For torrent part = It allows direct peer to peer connectivity without port forwarding.
For the future = IPv4 is running out, I heard some of lower unifi package (especially 10Mbps) will be NAT-ed soon ~.~

Double check router IPv6 settings again. Refer to screenshot posted few thread ago. Just to be sure.

Then reboot the router manually.
It will take around 5 - 10 minutes for router to allocate IPv6 address to your devices after pppoe is connected. (Because default AdvValidLifetime* of RADVD is 300 seconds)

I think slowly we will be IPV6 ready. It is like migration from http to https, takes a few years but eventually widely adopted.

U gotta say what speed u r on, when did problem started, what router before...

But yes, this tplink... many complaints.... but some hv no problem.

Multiple threads on this tplink router.

I have the same issue with you... same router tplink AC1200 given by TM.  although they change the modem and router (same model), the problem still exist.  called unifi CS.  They mentioned that my line got disconnected almost 30 times on average per day.  still waiting on their deep tech team to investigate the issue... this problem happened since 18 dec 2017....

I found that recently my torrent download speed very slow. 10mbps unifi , torrent download speed below 50kbps. Before this 500 -1000kbps. Anyone encounter this? Or Unifi now got limitation on it. I m using Xunlei.