In the fortress mine, there's a lift which is activated by setting four switches.
If the player has activated this lift, and then made their way to the top of the lift shaft (either by riding up the lift, or by taking the "hazardous" route), and then pushed the lift down to the bottom target, but then jumps off again to the platform on the left just after the lift has started moving down, and then deactivates the lift with the top switch, and then re-enters the central area of the mine (either by dropping down this lift shaft, or by taking the processing lift down and following the route of the previous big boulder run), then the player will become trapped.
It is still possible for the player to go along the "hazardous" route to reach the right hand side of the door at the top of the main lift - but, unless the player has a slime potion, it doesn't seem to be possible to get enough clearance to jump over the shaft from the right to the left. As a result, it's impossible to reach the top switch to re-activate the lift, thereby making the game unwinnable - see attached screenshot. The player will still have access to lots of save points throughout the fortress mine, though, and is likely to have saved their game several times before realising they are trapped.
Perhaps it's possible to escape if the player positions Edgar as far to the left of the door as possible without falling down the lift shaft, and then jumping, and then starting to move left no more than a frame or two later - but I've never succeeded yet, in spite of having previously completed the game with 26 secrets in under 20 game hours. I haven't tried reducing the maximum frame rate in the source code yet, though, or configuring the game to step through the frames manually.
But supposing it is impossible, I'd suggest that the best way to fix it is either to make the door to the right of the lift taller, or to move the door further over to the right, so that it's easier for Edgar to get the clearance necessary to jump over the lift shaft.