I noticed that what I see on the screen has sometimes nothing to do with reality.
Example 1: Screen shows really bright picture and "+3.0" but actual picture turns out way darker.
Example 2: Screen looks like I'm still at f/2.8 (lots of bokeh, very shallow depth of field) but I'm actually at f/8 and once I take the picture it has the expected, larger, depth of field.
In both cases the result is OK, but the preview on the screen is completely wrong. Why? I'm using Manual mode.
This sound trange. You might try to tell your local SIGMA SAV about this. IMHO it is a little problem but they will know better than me.