Vertical, dotted lines appear on the film output.

RESOLVE:

If the dots are a single vertical line, then that is probably the spiked tracker feed wheels (desktop models) of the printer leaving foot prints on the film as it steps through the wet ink.

Clean the printer and print a few pages to PAPER to dry up the wheels.
If the printer has been used “a lot”, its internal Waste tank may be full. That is not good as Epson would like you to replace the printer. You can check the internet for ways to OPEN the printer case and find the WASTE tank that is located under and behind the ink cartridges.