If the image looks correct in Qimage's live view but prints mirrored, the driver is mirroring it and therefore this is not a Qimage issue.
Of course this is the first thing I looked for and mirror was not enabled in the driver. A preceding and following print on smaller size would print normal.
The preview in Qimage was not mirrored either. One other thing I can think of is Windows 11 causing it, as I believe the 9400 driver hasnt been updated since 2021.
I don't see any reason to store a bunch of different resolutions because they are just going to inflate the file size without much benefit to other software that are not photo editors which can select individual TIFF pages... so might as well just turn it off.
I would never deliberately turn on this mode but as some clients and/or software do enable this, it is something I have to deal with every now and then. Anyway I figured it's good to be aware of this issue as it is not an obvious thing to look for and I've spent some time to track it down. It could help other people.