In the top there is 2 Chassis Assemblers, the lower one feeds the 3 lower Fit Body, while the top one only feed the top Fit body, it never feed the 3 others.
In the button there is the same there is 4 Fit Engine and 2 Fit Accessories. The 3 first only go to the first Fit Acc. while the top one only goes to the top one.
This make trafic chaos on the Conveyors, and all stations is connectet
(sorry for the size but the direction marking is hard to see at such crossings)
To solve this situation it could be usefull to merge/join the streams of 2 or assembly stations befor splitting up to the next step of the production line.
Here one example: