Solution
Check for anything binding paper together such as staples, paper clips, binder clips, or pages with bent corners (dog-ears). Click here for an illustration.
If problem persists, clean ADF pick rollers, belt and the separator roller.
To do this:
Open the ADF cover to expose the pick-roller assembly.
Clean both pick rollers and the belt with a lint-free cloth and a safe solvent such as isopropyl alcohol. Click here for an illustration.
With ADF cover still open, remove the green separator roller access cover as seen l.
Lift the tab(A) on the separator roll hub, and slide the separator roll off the shaft. Click here for an illustration.
Again, with a lint-free cloth and a safe solvent such as isopropyl alcohol, clean the separator roller as seen here.
Note: Do not use hard solvents or hand sanitizer to clean rubber surfaces.