A vertical streak on a feeder scan can come from a different imaging path than a mark on a flatbed scan. Comparing those paths is more informative than repeatedly changing the document's resolution or reinstalling the scanner software.

Use the same harmless page

Choose a clean page with enough printed content to reveal the line. Scan it through the automatic document feeder, then scan it on the flatbed if the machine provides both supported methods. Save both files and note the orientation.

Compare the line position and whether it exists in both results. If it appears only through the feeder, inspect the feeder scanning area described in the model's manual. That area may include a narrow glass strip separate from the large flatbed surface. A comparison narrows the investigation; it is not proof that a particular part has failed.

Epson's cited ADF cleaning guide explains how a line on a copy can help locate the corresponding dirty glass area. Use the diagram for your exact printer rather than guessing from another model's cover arrangement.

Clean only the documented accessible surfaces

Follow the manufacturer's power and cleaning preparation instructions. Use the specified cloth and cleaner, and avoid reaching into inaccessible mechanisms. Epson warns against spraying glass cleaner directly onto the glass, pressing hard or scratching the surface.

Do not transfer a glass-cleaning method to the feeder rollers without checking their own instructions. Materials and cleaning requirements differ, and a dry or unsuitable cloth may be wrong for a particular roller design.

After the area is dry and covers are closed, repeat the same scan. Compare the saved result with the earlier sample. If the line remains in exactly the same place, keep both files and seek model-specific service advice instead of increasing pressure or using a stronger solvent.

Before resuming a batch, check both sides of a duplex sample where supported. A clean first side does not establish that the second scanning path is also clear.

Sources: Epson ADF cleaning and line location.