S6: sudden battery drops + boost no longer working

I have got a brand new S6 and I'm running into a couple of issues.

First, the battery sometimes drops suddenly. I've read here that this is common during the first couple of weeks, so I'm not too worried about that one yet.

The more annoying problem is that boost doesn't work anymore. At first I thought it had been deactivated because of low battery, but I charged it to 90% over a full weekend and it still won't kick in.

I bought it at a local store and can bring it back there, but that'll take some time so I figured I'd ask here first in case anyone has run into the same thing or has an idea what's going on. Thx