Apple has revealed that "certain models" of internal SATA drives can be dismounted by the New Mac Pro.
The new 2023 Mac Pro comes with slots for PCI-E expansion cards, but due to the design of Apple Silicon, it can only support a limited number of types of card. Chiefly it can be used for extra storage, but now Apple has revealed that there can be a problem with even this.
"Certain models of internal SATA drives might unexpectedly disconnect from your computer after your Mac wakes from sleep," says Apple in a new support document. "This can occur if your Mac automatically goes to sleep or if you manually put your Mac to sleep."
"If you see a message that your disk was not ejected properly," it continues, "you can restart your Mac to reconnect to the drive."
The problem is specifically with internal SATA drives, but Apple is not more precise than that. There's no detail yet over which models are involved.
Apple says that it "is aware of this issue," and also that a "resolution is planned for a future macOS update." Unusually, the support note also says that "this document will be updated as more information becomes available."
In the meantime, Apple Support offers a workaround, which is to turn on the System Settings option, "Prevent automatic sleeping when the display is off."