The version of macOS the given system has a bearing here. One of your systems might still be running macOS 10.12.5 (Sierra) which was the last version of macOS which used HFS+ and your other system is using MacOS 10.13 or newer. which uses AFS. So the given systems firmware doesn’t have the needed update to boot up under AFS.
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The version of macOS the given system has a bearing here. One of your systems might still be running macOS 10.12.5 (Sierra) which was the last version of macOS which used HFS+ and your other system is using MacOS 10.13 or newer which uses AFS. So the given systems firmware doesn’t have the needed update to boot up under AFS.
To overcome this you’ll need to re-install your OS to allow the installer to update the systems firmware. You can do this using Internet Recovery or using a bootable OS installer drive setup from another Mac with the OS version you want to use (I recommend you upgrade to Mojave 10.14.x as its better than High Sierra 10.13.x)
The version of macOS the given system has a bearing here. One of your systems might still be running macOS 10.12.5 (Sierra) which was the last version of macOS which used HFS+ and your other system is using MacOS 10.13 or newer. which uses AFS. So the given systems firmware doesn’t have the needed update to boot up under AFS.
To overcome this you’ll need to re-install your OS to allow the installer to update the systems firmware. You can do this using Internet Recovery or using a bootable OS installer drive setup from another Mac with the OS version you want to use (I recommend you upgrade to Mojave 10.14.x as its better than High Sierra 10.13.x)