Not sure, what exactly happens
From the error message, it is when deconstructing an entity, presumably an underground belt or pipe, and "Underground indicators Fixed" fails to find the other partner of this belt.
The error itself happens in "Underground indicators Fixed" after autobuild calls player.mine_entity, so I would point in that direction. But I don't want to exclude, that autobuild might do something "forbidden", which the other mod should not have to handle.
