The mod Belt Balancer 2 (2.0.9) caused a non-recoverable error.
Please report this error to the mod author.

Error while running event belt-balancer-2::on_player_mined_entity (ID 74)
belt-balancer-2/objects/part.lua:215: attempt to index local 'belt' (a nil value)
stack traceback:
belt-balancer-2/objects/part.lua:215: in function 'remove'
belt-balancer-2/control.lua:145: in function <belt-balancer-2/control.lua:134>

I agree. I also encountered this bug with one balancer element (I'm deleting the entire base, but only with one for now).