I have seen this type of issue before where it only drops out on the left side of the print and it ended up being the manifold was clogged and restricting ink flow. You could take the manifold off and flush it but that can be time consuming and it could also damage the head if you aren't careful. You could also try running a long store cycle. This will empty the machine of ink, flush it out with cleaning cartridges and then you can fill it back up. This is the more expensive option but it is safer then flushing the manifold.
Also, you should change the dampers to rule them out.