On my Manjaro 15.12 install Plasma 5.5 seems unstable.

In particular, two things happen:

1. If the screen goes dark after some period of inactivity, Plasma crashes, and when the mouse is moved and the screen comes back to life, I see an error message telling me Plasma has crashed.

2. If the lockscreen is activated after some inactivity, and I move the mouse, one of two things happens:

a
- either Plasma and/or KRunner crash. If KRunner, I need a system restart because everything goes dead.

b
- or, on entering login details, I get don’t get past the error screen and a message appears saying “KDE is already running”, after which everything goes dead, except the mouse cursor.

These problems seem completely independent of any programs I may have up and running at the time. (E.g. if I boot, login and leave it for 5 mins, the screen goes black and I get problem 1). It also happens on, essentially, a fresh install. Also it happens on the development version Manjaro 16.06. It does not happen in other desktop environments (e.g. Cinnamon or Gnome).

For the moment, I have disabled the lockscreen from kicking in when I am away. Obviously, in the long run, I would prefer to have this for security/privacy reasons.

How can I overcome these problems?

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Some details:

I am running kernel 4.4.2. However, the same was true on 4.1
I have an NVidia GTX 780 Ti running proprietary drivers.

These are the only 2 differences vs the “stock” install from the 15.12 Capella iso.

The rest of my system: Asus Z87-AR, i7 4770k, 32 GB Ram. That's about it.

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Thanks in advance for suggestions.

Latest set of updates fixed this.