That can be solved by opening the disc using VLC when makemkv is scanning. VLC will free up the lock.
I’ve been wrestling with something similar for a week lol.
There’s a thread about the error on the makemkv forums. And I’ve personally salvaged discs this way only yesterday.
Also, makemkv can open a DVD as a raw data file. Mine were old TV shows so I was able to pull the individual episodes avoiding the errors or at least getting some if one was corrupt. I saved an additional 3 discs this way.
One last method if you can set the speed of the drive to 1x; rip slow and set lots of retries (5) to maybe give it a slightly better chance. 1x was always the most reliable. Any speed over and you have mixed results.
Lastly, there’s a list on the net about best drives. If you really care and want to throw $100 at it, pick one up. The drives for $20 you find on Amazon won’t read anything a few years old. Theirs lasers are garbage compared to ones manufactured 10+ years ago.
riley0