Hi tmartinac,
Thank you for using the Support Forum. Make sure you are using the latest driver for your printer. Uninstall the one you have now and then reboot the computer. Install the most recent driver. Make sure you have the latest firmware for your printer. If you are not using the latest firmware from November 2020 please consider upgrading your firmware. If none of this helps please consider contacting your support centre for further assistance.
We are trying to print from a Redhat server to a AltaLink® C8135 but every print sent to the MFP is printing duplex. I have attached our default settings on the linux server. We have also looked at every section we could think of on the MFP's settings and everything feels like it is set to single page. We did install the driver per the instructions on this page.
https://www.support.xerox.com/en-us/article/en/2121938.html
Any thoughts on this issue?