Thanks for all your answers. I really do appreciate you taking the time. We have now ordered a Summa DC5 and we will install it from next week. As we have no technical support on it. it should be interesting to see how long it will take us to figure it out.
We couldnt justify fixing the gerber as it was already way too much work using it.
Fred is on the right track with his initial suggestion.
Not a blown pixel or damaged print head as your other foils are laying down properly along the same axis (you would see the same line continue in other prints).
Although possible, I am skeptical that this is a damaged printhead data cable as you typically you would see a missing zone rather than a single line. Could be a buffering issue caused by a failing communication still elsewhere though, maybe the mainboard? If you can disable foil conservation this may circumvent the issue but you will blow through your blue cart.
Check your cartridge for how much is consumed. Sometimes when 75% of a cartridge is used up the foil can bind after larger prints due to friction or mechanical failure (clutches, motor, power supply) affecting the foil drive mechanism; however, if this is consistently in the same spot on every print it indicates a communication issue.