For some years, yes, years, my OM-D struggled to start up properly! Once alive, the picture were as good as always. What is going on? Personally, I get a sense of planned obsolesce, in particular since many more appear to be complaining about the same failure my OM-D exhibits.
Some additional searching revealed a solution found by some: set the camera to burst mode. It might fail a couple of times, but will continue in single frame mode eventually.
I can confirm that this will work initially.
However, once the camera is switched on again, the good-ole black-out will return.
By now, I experimented with switching the camera back to high speed burst mode, before turning it off. The next power-up will again lead to a black-out of the camera. Restart yet again appears to be leading to a camera that actually does not shut off immediately... up to now, this appears to be woking, i.e. booting the camera will result in a functioning device.
I am close to discarding the OM-D and abandon Olympus all together, in favour of the new Panasonic cameras employing IBIS.
By now, I can only share positive experiences using the Lumix GX85.