Uneven colour on print Mimaki

So, I have this printer, Mimaki UJV55-320. I print on thick plastic fabric (the ones used for truck covers). Sometimes I get uneven colour in a pattern of perpendicular lines on the direction of the print. They almost look like they are in the same line and distance with the pinchers. I tried all sorts of things to get rid of them, but nothing really works. If I stretch the fabric with my hands it gets a little better. The vacuum is at max, I have cleaned the suction tray and the ventilators, the fabric is mounted on the machines feed-take up system, so it keeps it in a fairly tensioned state. Can it have anything to do with the pinchers? Is there anything I can do about it? The machine is about 3 years old. Nothing has been changed, there was no check-up or maintenance done, except the classics head, nozzles maintenance. Changed the mist filter ... You can see in the picture some yellow vertical lines, like the blue didn't fall there or less blue fell