The mod Underground heat pipe (2.2.0) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event underground-heat-pipe::on_built_entity (ID 6)
underground-heat-pipe/control.lua:58: attempt to index local 'old_entity' (a nil value)
stack traceback:
underground-heat-pipe/control.lua:58: in function 'bring_heatpipe_to_front'
underground-heat-pipe/control.lua:285: in function 'check_for_neighbours'
underground-heat-pipe/control.lua:294: in function 'update_mode_for_all_pipe_to_grounds'
underground-heat-pipe/control.lua:232: in function <underground-heat-pipe/control.lua:199>

reproduction steps?

I think I did it with editor on, and I can't reproduce it now with it off, so I have no idea. My only assumption is that I picked up some part of underground belt I shouldn't with Q and then when I placed it your mod freaked out.