Last week I purchased a Sony A7ii, which I absolutely love.
The camera is fantastic for some many reasons that are covered by many reviews. Unfortunately I was hit by small known issue with some of the camera builds: sometimes, after you take a picture, the shutter will get stuck, and stay closed.
The symptoms of this are easy to see. After you take a shot, the LCD display turns black. If you try to take a picture, the camera reports "camera error turn power off then on."
Of course, turning the power off and on doesn't actually help at all. Neither does cleaning the sensor.
You can usually nudge the edge of the shutter upwards very gently to get it to release.
After switching lenses several times with no improvement, I was demonstrating the issue to my wife without a lens attached.
Immediately the shutter stopped getting stuck!
I reattached the kit lens, and another lens, and still the camera has been fine.
So if your shutter is getting stuck, try taking a few shots with the lens off in a clean environment - you don't want to get the sensor dirty!