After a rip I have noticed that discs (Bluray in this instance) will not eject when I press the eject button on the drive. It will act like it's going to eject, and then it's 'reloaded'. MakeMKV then tries to re-read the disc. The same happens if I click the 'eject' button from the MakeMKV toolbar. If I click the toolbar button repeatedly, then eventually Windows explorer will attempt to open a file window. Once it blocks MakeMKV, the disc will eject from the drive.
I can also eject the disc if I just exit out of MakeMKV but this is not very helpful since then I have to re-load it to process more discs. It didn't use to behave like this and the fact it happens on different drives leads me to believe it's not drive-related but an MakeMKV bug.