Epson WF4820 printer duplex problem

[chemistry]

Mrs chemistry's Epson WF4820 inkjet has suddenly stopped printing doubled-sided output. Instead it prints any two page document with the first page 'normal' and then a second page on a second sheet, upside down (as if it had tried to flip/duplex it, but failed, so printed on a second sheet instead) - see left hand document(s) in picture.

Printing the same document from the same computer (Macbook running 12.5.1) with the same settings (Layout etc.) on my similar Epson WF4830 works perfectly - see right hand document in picture.

Her printer has up to date firmware etc., so I'm at a loss to explain why this is happening and to know how to fix it. I'm pretty sure it's a printer issue rather than a problem with the laptop (since the laptop prints double sided documents fine via other printers on the same home network, as evidenced above). Unfortunately I can't find any 'duplex' (or similar) settings in the printer's menus.

Can anyone help?

[Dave Hedgehog]

does it have a book printing mode?

[Greenmantle]

My current laser printer had that issue.
Called in a guy for a service and clean.
The cogs get dirty and so are unable to complete the complex duplex motion.

[chemistry]

Fixed!

It turns out the paper in the tray had been set to the wrong setting (inkjet photo glossy, not plain).

Thanks for the help.