Since the 4.1.0.868 update of mid-November I have the problem that music stops playing a few minutes into a track.

Might be the 1st track or the 10th, no obvious pattern.

A couple of times I have seen a message saying that Spotify is using excessive battery power, so Android system has closed the app.

I have not updated any settings or system.  Using an LG G3 with Android 5.0 (since many months).

Also have the play restarting when I unplug headphones/speakers problem since the mi-November update. (as is being reported by many people).

Spotify dropped a big clanger with this update. There'd better be  a fix and update SOON!