In multiplayer, a player accidentally connected a blue belt elevator to a red belt elevator. This connected pair of elevator pieces became impossible to edit or remove. If you attempted to remove either piece, your game would crash. If you attempted to rotate a piece, you would get a different crash.

The crash logs are as follows:

The mod Subsurface - build beneath your base! (1.1.24) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event Subsurface::subsurface-rotate (ID 268)
Subsurface/scripts/elevators.lua:25: attempt to index field '?' (a nil value)
stack traceback:
Subsurface/scripts/elevators.lua:25: in function 'switch_elevator'
Subsurface/scripts/elevators.lua:158: in function 'elevator_rotated'
Subsurface/control.lua:906: in function <Subsurface/control.lua:900>

-and-

The mod Subsurface - build beneath your base! (1.1.24) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event Subsurface::on_player_mined_entity (ID 74)
Subsurface/scripts/elevators.lua:270: bad argument #1 of 2 to 'ipairs' (table expected, got nil)
stack traceback:
[C]: in function 'ipairs'
Subsurface/scripts/elevators.lua:270: in function 'elevator_removed'
Subsurface/control.lua:647: in function <Subsurface/control.lua:643>