I have the same issue. My 3345 is new (3 months old) and never scaned duplex under windows. BUT it is scanning ful duplex on my Android phone. So it's not a printer issue, its a low quality driver.
I have the same problem but in my case the printer is new and the option to scan both sides is not available in the expirience app. Could you fix it?
Sounds like you have tried everything already, so it would be a hardware escalation: 1-800-821-2797 or 1-800-835-6100.
Hello I used to scan remotely from my pc a lot of documents from Xerox prind and scan experience. Everything was working correcly (I could scan 2-sides of paper) until last few days. Right now this app (other don't even find any scanner driver) scanning only one side of each paper which is useless because if needed i would put it on glass. Tried a lot of things : update drivers, install dedicated scan drivers, reinstall apps, search option in web panel (in experience app this option is unavailable).