Hi @RickfromtheMill,
Welcome to the HP Support Forums! I see by your post that you no longer have the A3 paper size, after a Windows Update. I would like to help you out today. If this helps you to reach a solution, please click the "Accept as Solution" button down below in this message. If you wish, to say thanks for my effort to help, click the " Thumbs Up " to give me a Kudos.
Most likely the Windows Update changed the print driver.
You may have to do a System Restore back to when everything was working properly, Recovery options in Windows 10.
Once the printer is working is working properly again, the option would be to ignore the printer software updates or you can try these external resources, that have some advanced steps. This information was provided by my co-worker @midnight-anwrs.
One poster tried the Show or hide updates and it resolved their issue.
You can also give feedback to Microsoft and hopefully they will release an update to correct the feature in the operating system. You can learn how here; Updates and feedback.
Here is a document to manually create a custom paper size, if you still don't have the option available: HP Printers - Creating Custom Paper Sizes.
You can always install a generic driver to do the custom sizes.
From the start up screen, (tiles menu) type in "Devices and Printers", select settings,
click on Devices and Printer.
Click add a printer.
Go through the wizard.
Select HP from the first list.
Select the Officejet Class driver from the list.
Apply settings.
Check your settings, and try printing again.
Please post the results. I look forward to hearing from you again. Thank you.
Gemini02
I work on behalf of HP
Click the Thumbs Up below to say “Thanks” for helping!