Mojave on Mac Pro 5,1 diskutility hangs if a hard drive on SATA bus in Optical bay is unmounted.
Something about Optical bay SATA buss 5 or 6 the does not like a hard drive connected.
I am running into issues with the GUI Disk Utility. This is not occurring with cmd line diskutil. Everything is ok with a good disk mounted there, and Disk Utility will initially work with it after a full system reboot. But if the disk is ejected through the finder, launching the GUI version will hang "loading disks". Also hangs if the GUI is used for first aid or formatting, as first action is to unmount.
If cmd line is used to mount the drive, then GUI will run OK after forced quit & relaunch.
Mac Pro, macOS 10.14