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When connecting a HDD, USB device or SD card to the Mac while the software is running, the disc stops spinning and the copying process can't be continued. The software doesn't reconnect to the drive even when returning to the track selection menu. All titles that have been entered here are therefore lost for the session.

MakeMKV 1.10.4
Mac OS X 10.11.6
Optical drive: LG BP40NS20 (Firmware ML04)

What happens if you're playing a video from a DVD and do the same actions?

What you describe would usually be attributed to the operating system getting "lost", but it is hard to test that, except by performing similar actions.

It only affects MakeMKV, tried the same while playing a DVD and there was no issue.