To me it looks like there is break in the over head rail on that side of the production line, having said that it looks like there is a break on the other side as well, the side that is working does that get supplied from the paint booth end of you production line rather than the starting importer before the production line starts?
The green lines suggest it should be linked. Does it go away after a second or two? is your PC really low spec? the game takes time to figure out new routes, but normally its only a second or two.