TL;DR; I checked the dummy cartrige and primed it again.
When I had issues with my EcoTank, I took out the dummy cartrige and checked it. The reservoir was completely empty, so I had to prime it again. I actuated with a screwdriver the valve at the bottom and put a bigger suringe through the rubber lid of the EcoTank. By “opening” the vale of the dummy cartrige and pushing air through the suringe into the tank, pushing some ink back into the dummy cartrige to prime it again, I successfully recovered all my dummy cartriges and my printer is working flawlessly since then :3
At least in my 2650, on the moving part in the printer are 4 individual white ink cartriges, where the ink hose is attached to.