The lines are most likely caused by dye blobs accumulated on the printer head.
You can clean the head with some isopropyl alcohol and q-tips and your prints should look flawless again.
In my case this never actually fixed it, because halfway through a test print page they reappeared again, but finally I found a permanent solution.
What to do if cleaning the head doesn’t work?
I found out that, if when you clean the head blobs appear instantly again, its caused by the roll having dust (although its not visible on visual inspection)
To clean it get some cello tape, but make sure its the ones that don`t leave residue
Make a loop and start going through the paper feed roll, like when you remove dust from phone screens before applying a screen protector. Dust(and other gunk) should stick to the tape, leaving you the roll clean.
Having particles probably changed slightly the paper position, making it be too close to the head and the ink from it accumulated on the resistances of the head.
After cleanup your prints should be in mint condition again!