Why is Macbook Air 2014 crashing bi-monthly, startup disk missing and OS Re-install required?

Use Apple Diagnostics to test your Mac - Apple Support

You can run Apple Diagnostics on just battery power, but try to find a power adapter with an intact cord.

Samathustra wrote:

Mac Air 2014 running 11.6.4, recently upgraded with OWC Aura 240GB hard drive and battery. Power cord is also frayed.

Each crash results in a missing startup disk-- file folder with question mark. Opt-Cmd-R for internet recovery. Attempts to repair disk in Disk Utility work fine, but doesn't fix the startup. So I have to format, reinstall OS and migrate from backups.

Obviously there are many potential issues. Any ideas? List to troubleshoot?

Did you try to reinstall macOS over top of itself instead of erasing the drive?

Do you get a Kernel Panic error log when booting the Mac after this happens? If so, having the Kernel Panic log may contain clues to what happened.

Try running DriveDx to check the health of the SSD. Post the full DriveDx text report here using the "Additional Text" icon which looks like a piece of paper.

I find that the SSD tends to be the weakest link assuming that you don't have a software issue that is corrupting macOS. However, since you now have two SSDs that appear to have the same issues, then it may indicate a bad Logic Board.

Yes, those "Media and Integrity Errors" are concerning. You should contact OWC tech support and tell them about the repeated blinking folder with question mark issues and mention the "Media and Integrity Errors" from the DriveDx SMART report. I think with both of these items OWC will replace the SSD under warranty for you.

Samathustra wrote:

I also re-ran DriveDX and now there are no errors showing there either. All results are good.

The errors should not just disappear, although I have seen the original Apple SSDs not retain the results of the SSD's selftests after a reboot. I've never seen that with a third party SSD though.

I'm curious why the crash causes the startup disk to disappear, when it is still visible in Recovery Mode.

Something is causing the OS on the SSD to become corrupted. My guess would have been those "Media and Integrity Errors" since that indicates stored data would be corrupted. However, there is a slim chance you could have more than one problem with this laptop such as a bad Logic Board.

OWC tech support has offered to fix or replace the drive. I don't know if I'm wasting my time anymore.

Without actually being able to see the laptop physically I cannot say if there may be more going on here. If the Logic Board and the rest of the laptop is in good working undamaged condition, then the SSD would be the weakest link. Obviously OWC feels the SSD may be bad since they offered to replace it. Companies don't usually offer to replace things unless they feel the item is likely defective with the information you've provided to them.

From the Kernel Panic log:

nvme: "Fatal error occurred.

This usually indicates a bad SSD. There is a slim chance you may have a bad Logic Board or you have some third party driver installed that is interfering with the macOS NVMe driver (I don't see anything in the backtrace regarding third party drivers), but 99% of the time which I've encountered this error with our organization's Macs (and helping others here on the forums), the SSD is at fault.