I was required to update to Sierra to get Xcode on my machine. I did that yesterday. Currently it stands at:
Version 10.12.4 MacBook Pro (Retina,13-inch, Early 2015) Processor: 2.7 GHz Intel Core i5 Memory 8 GB 1867 MHz DDr3
After this update,when my Mac goes to sleep or is shut down, about half of the time it displays the flashing ?, prompting hand-wringing from me. I start going through all of the steps for system restore, but often the SSD is not located during the system restore, and when I restart again maybe the mac finds the SSD and starts up normally. This is very annoying behaviour, of course.
I have had the flashing ? before, and I took it to an Apple service center in Trondheim where they held it for a month before returning it to me, with the diagnosis that the hard drive had unmounted physically and all that was required was re-inserting it. Great. Glad that took only a month.
I am tempted to believe that this is a physical hardware issue where the hard drive is experiencing intermittent hardware connection. But I've never experienced it shutting down in use, as you would think would happen if it were something like a loose connector, which makes me doubt this hypothesis.
I asked this question on the apple forum, and I'm going to be reprimanded for the solution that I'm leaning towards: removing the back panel myself and staking the hard drive to the connector with adhesive. Taking it to a service center is unworkable for the following reasons: a) Because I'm currently on a Greek island in the middle of the aegean, and b) because I can't afford to lose my Mac for a month again for some tech to do what I want, which he probably won't because staking a hard drive isn't in the Apple book.
Any ideas here? I mention the Sierra update because of course, a lot of signs point to that, but the intermittent startups make me think that is circumstantial.