Mac Pro running Catalina cannot recognize other bootable external volumes at startup (left option)
Greetings,
My 2013 Mac Pro has lost its ability to mount external boot volumes. The issue could be the Mac Pro, or it could be that the other OS volume has some sort of corruption with startup files, but, here's the scenario:
The Mac Pro is running Catalina. The external drive has a fully functional High Sierra installed on it and will easily mount in another older Mac Pro, appearing to be healthy and fine. It is connected to the Catalina Mac Pro via Thunderbolt 2.
1) When I start up pressing the <left option> key, the startup menu only recognizes the Catalina volume.
2) If, in Catalina, I go the "Startup Disk" Preference pane, it sees both volumes (Catalina and High Sierra) - I can select High Sierra is a startup volume. However, on subsequent boot up, that volume is not seen and the Mac reverts to booting up in its "native" OS of Catalina.
All was well until a few days ago, now I have this issue.
Any advice or direction would be much appreciated.
Thank you,
dncollins
Mac Pro, 10.15
