Option eject media after session is always grayed out on Drive-Definitions for ACSLS or SCSI Libraries. Only Relevant for Stacker-Devices if I'm not mistaken.
Main Problem is that your Sessions don't rewind and eject the Media at Job-Completion, haven't seen that behavior so far.
Can you share your Library and Device config (omnidownload -device LogicalDevice & omnidownload -library Library) as well as a Session-Report from one normally running Job (without Busy-drive fault)?