brake noise and transmission’s problem.

I bought my new Legacy less than one month and took good care of it.But now there are two issues that bothers me.
1.It makes a clunking sound when I take my foot off the brake pedal after a complete stop.It is really annoying.
2.Can not speed up after starting.Really dangerous.
Last weekend I parked my car outside for about eight hours,it's 0 ℉. Around 8 pm I started the car,the idling revving is around 1800 RPM. I waited the car to warm up until the Blue Alarm of Engine Cold turned off. Then I drove about 2 miles to the toll way. When I pushed accelerator,it got very sluggish. The max speed just can reach 30 to 40 mile. The RPM was above 2000. If I continued to push the accelerator,the car vibrated badly and RPM to 2500. It can't speed up.
It seems it's stuck in a lower gear like third and fourth. Even I tried to manually shift the cvt, but it can't go higher than 4th gear. The tire pressure is normal.
I restarted the car, same problem happened. I pulled over and called Subaru road assistant. The police came and led us off highway. We waited about half hour, the car became normal, and we drove home.
Until now, the same issue happened twice. It seems randomly and the dealer said they can do nothing right now.
I would like to know what the cause is, like quality and deficit; and how we we can solve the issue.Because I was stuck on the highway for one hour,and don't want deal with the situation again.
Can anyone give me some advice?