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MacBook Pro SSD not mounting; OS unstable

After 2 years of flawless operation, I awoke to a very hot laptop which, upon opening the lid, had a blinking question mark folder. Cycled power and everything worked fine.


After that incident, the blinking folder would reappear if the computer was left idle. Took the laptop, 2017 MacBook Pro with 2 Thunderbolt 3 ports, to the Genius Bar and was told that the hardware checked ok and that a system reinstall might help. I made a bootable installer thumb drive with Mojave, as I had no problems prior to Catalina, and proceeded to reformat the SSD. Computer booted but Disk Utility did not show the SSD for the Mojave install.


I randomly got the SDD to show after closing the lid and promptly reopening it. I was able to install Catalina from Internet recovery.


Now, when I power-on the computer, it has the blinking question mark. Control-R yields a successful boot to Disk Utility where all that is shown is a disk image.


If, at that point, I shut down the laptop, close the lid and after 20 seconds open it back up, I usually get a Catalina sign-in page and Disk Utility shows the SSD!


I have been through all of the NVRAM and SDC reset procedures. What do I need to do to get the computer to mount the SSD on start? When Catalina is running, the SSD shows in System Preferences<Startup Disk. When I boot from the thumb drive and it asks where I want to install Mojave, all it shows is the external drive. Thanks in advance for your help.




MacBook Pro

Posted on May 10, 2020 9:18 AM

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Posted on May 10, 2020 9:41 AM

Two very simple things to do. To install a different version of macOS than what is installed, you must first erase the drive. Second, a boot volume needs to be formatted using Mac OS Extended, Journaled. If you are installing Catalina, then the disk must be formatted using APFS if it is an SSD.


Install El Capitan or Later from Scratch


If possible, back up your files.


  1. Restart the computer. Immediately, at or before the chime, hold down the Command and R keys until the Apple logo and progress bar appear. Wait until the Utility Menu appears.
  2. Select Disk Utility from the Utility Menu and click on the Continue button.
  3. When Disk Utility loads select the target drive (out-dented entry w/type and size info) from the Device list.
  4. Click on the Erase button in Disk Utility's toolbar. A panel will drop down.
  5. Set the partition scheme to GUID.
  6. Set the Format type to APFS (SSDs only) or Mac OS Extended (Journaled.)
  7. Click on the Apply button, then wait for the Done button to activate and click on it.
  8. Quit Disk Utility and return to the Utility Menu.
  9. Select Install OS X and click on the Continue button.


APFS can be used with Mojave or Catalina.

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Question marked as Best reply

May 10, 2020 9:41 AM in response to DGangwer

Two very simple things to do. To install a different version of macOS than what is installed, you must first erase the drive. Second, a boot volume needs to be formatted using Mac OS Extended, Journaled. If you are installing Catalina, then the disk must be formatted using APFS if it is an SSD.


Install El Capitan or Later from Scratch


If possible, back up your files.


  1. Restart the computer. Immediately, at or before the chime, hold down the Command and R keys until the Apple logo and progress bar appear. Wait until the Utility Menu appears.
  2. Select Disk Utility from the Utility Menu and click on the Continue button.
  3. When Disk Utility loads select the target drive (out-dented entry w/type and size info) from the Device list.
  4. Click on the Erase button in Disk Utility's toolbar. A panel will drop down.
  5. Set the partition scheme to GUID.
  6. Set the Format type to APFS (SSDs only) or Mac OS Extended (Journaled.)
  7. Click on the Apply button, then wait for the Done button to activate and click on it.
  8. Quit Disk Utility and return to the Utility Menu.
  9. Select Install OS X and click on the Continue button.


APFS can be used with Mojave or Catalina.

May 17, 2020 10:22 AM in response to DGangwer

I can offer this solution that is supposed to install the original version of macOS that came pre-installed from the factory. Give it a try by installing it on an external drive and use Option booting to give it a test. Or just put it on that SSD.


Internet/Network Recovery of El Capitan or Later on a Clean Disk


     If possible back up your files before proceeding.


  1. Restart the computer. Immediately, at or before the chime, hold down the (Command-Option-Shift-R) keys until a globe appears.
  2. The Utility Menu will appear in from 5-20 minutes. Be patient.
  3. Select Disk Utility and click on the Continue button.
  4. When Disk Utility loads select the target SSD (out-dented entry w/type and size) from the side list.
  5. Click on the Erase button in Disk Utility's toolbar. A panel will drop down.
  6. Set the partition scheme to GUID.
  7. Set the Format type to Mac OS Extended, (Journaled.)
  8. Click on the Apply button, then click on the Done button when it activates.
  9. Quit Disk Utility and return to the Utility Menu.
  10. Select Install OS X and click on the Continue button.


BTW, is the SSD an Apple product or other manufacturer?

May 16, 2020 7:59 AM in response to DGangwer

I have have followed Apple instructions on reinstalling OS. It is clear that the erasure of the SSD is not 100% as High Sierra is still resident in the Recovery partition. (How is there a partition if the install created APFS format?)


On boot, the computer does not mount the SSD. If Internet Recovery is used, the computer boots but, again, does not mount the SSD. If external boot/install drive is used, computer boots, but there's no SSD in Disk Recovery. If you try installing OS in Disk Utility, there is no internal drive for the installation depicted.


However, after initial boot, if the computer is shut down and the lid closed, it magically is ready for sign-in upon opening within a minute. At that point, the computer functions fine as long as it is being used. If left idle, it sometimes heats up with a blinking folder/question mark.


When the computer is running properly, it shows the SSD as the start-up drive in System Preferences. During the unsuccessful start-ups, the Start-up disk selection window is empty.


Do I need to use Terminal commands in order to truly zero out the SSD and start from scratch? Clearly the Disk Utility erasure did not do the trick.



May 16, 2020 12:47 PM in response to DGangwer

High Sierra will not create an APFS drive because it cannot write to one. If you install High Sierra, then you need to use Mac OS Extended, Journaled. Read my instructions from earlier at the end of which I stated, "APFS can be used with Mojave or Catalina."


Internet Recovery can be used to install the current version of macOS or the version that originally came pre-installed when new from the factory. If you wish to install the same version you were running, then boot from the Recovery HD.


You do not zero out an SSD unless it is truly a necessity because doing so will shorten its life.

May 17, 2020 10:11 AM in response to Kappy

At this point, I would rather have a shorter life with a computer that works as opposed to the haphazard boot sequence I am dealing with now. In fact, if I could find one, I've been temped to replace the SSD in an attempt to rectify this nonsense.


Perhaps I wasn't clear before: Mojave was installed from the external boot drive, thus APFS was selected for the SSD erasure. High Sierra is resident in the Recovery drive. The reason I downgraded from Catalina to Mojave was many users tied overheat/boot/blinking question marks to Catalina. Mojave has not fixed the OS instability.


Bottom line is that if I boot from Internet Recovery or the external drive, there is no SSD depicted in Disk Recovery to install the OS. Historically, I have fixed these types of issues with a clean install on PCs and have never had to do so on an Apple product. I was intrigued that Apple had a recall on smaller SSDs in the non-Touchbar laptops but not the larger ones.


The computer works fine once it is tricked into doing so. I simply want it to work like it did out of the box.

May 17, 2020 10:57 AM in response to Kappy

Thank you for your help. I will do so ASAP.

The drive is Apple original. I am intrigued that replacements aren't available.

FYI - I converted my old MacBookPro to SSD when its hard drive failed. It was a painless and productive upgrade. I was, thus, so looking forward to my new laptop with an SSD as original equipment. It provided a couple of years of faithful service until now. Internet research indicates I'm not alone with heat, boot and OS stability problems.

Thanks, again, Kappy!

May 20, 2020 7:02 PM in response to DGangwer

Installed High Sierra to no avail. Exact same symptoms: Boots to a blinking folder; Internet Recovery gets to Utilities but there is no internal drive to install OS; External boot does the same. Randomly, closing the lid and reopening yields a booted laptop ready for sign-in.


Any last ideas before returning to the Genius Bar?

MacBook Pro SSD not mounting; OS unstable

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