The last idea may yet be the one to adopt.
Other than suggesting to see if the printer has a Factory Defaults option, take it to another computer and see what happens or depending on its age, ring the manufacturer and see if they can suggest any solutions.
Printers seem to get weird and do all sorts of odd things as they age like picking up another sheet part way through a print or sitting there like a lemon doing nothing but if you press print again, it will print at least 2 copies straight away.
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