MacBook Pro external disk repeatedly ejects and remounts

Memoire wrote:

Thank you, D.I. Johnson, for your reply and advice.

As the cable came with the Passport External HD and has worked to now, I tried to connect the drive to the other USB connection, and the drive seems stable and is not unmounting like previously.

A different external HD doesn't have the same issue of being unmounted in the USB socket that has issues with the Passport drive.

Seems your solution worked.

FYI, the cable connector may be wearing out along with the USB-C port on the Mac. The USB-C ports on the 2016-2017 Macs had a huge design flaw where the board edges which helped to keep the cable snug would quickly wear down causing loose intermittent connections. Ideally the cable should be snug when attaching & detaching from the computer & even the drive.

We see this very often and the typical culprits would be the cable or the connection point. Sometimes it's the drive hardware actually having a problem.

You can check if it's a cable problem by using a different, good quality cable. If you are using any sort of plug adapter, then I suggest you consider buying a cable that has the correct plug at each end for your device and your Mac. That would be USB-C at the Mac end and could be one of several at the ext drive end - USB-A, USB-C or maybe USB-microB. Check the user guide for your particular drive.

A connection point issue can be troubleshot by connecting the drive to a different port on the Mac. If you are connecting the drive via a hub or dock, then bypass that and connect directly to the Mac. If using a hub or dock, that dock should be self-powered via its own ac power adapter and not bus-powered by the computer.

The drive itself may get power from its own ac adapter, which should provide whatever it needs regardless of the connection point.

If the drive is a small notebook-class drive, the check the power required and power available for the device by visiting the System Information app. Press the Option key and click the Apple menu  > System Information.

Under the heading Hardware, click the USB line to see the particulars. If there is little or no headroom between 'Current Available' and 'Current Required' then you may have issue with the drive remaining connected under load.

You're welcome.

🤞🏽