Thank you for using the Support Forum. Please take a look at this solution for printing on custom size paper. Also make sure that you have the top and bottom margins for your document set properly in the program you are using on the PC. The printer has specific print areas please see this solution for those specifications. If the margins are just a little out of spec it could cause the extra page to "print". If this does not help please consider contacting your support centre for further assistance.
I have a ColorQube 8700x and I'm trying to print a custom sticker from the bypass tray.
I have everything working except for each print I get a second blank page printed on 8.5 x 11 for every sticker I print.
I have confirmed the custom size in the bypass tray and set the page set-up to match my custom size and set the paper tray to tray1bypass for each job.