I had this problem, I learned only today that it is linked to the recent version 4.0 firmware update. So, if you have the same issues you need to install the new firmware 4.01 which returns the camera to pre version 4.0
In my case the fault appeared as a freezing of the whole camera and all functions. The EVF froze with an image of the last view the camera had and even switching the power off wouldn't clear it. I have to remove the battery to reset. This happened 3 times, then disappeared.
We then will need to wait until version 4.02 is made available to install the new features. I am quite keen to try the focus stacking feature.