We ran into this issue last year on, the response from IBM was;
If they are using "Autosize" for their Paper Size, that would be the issue. Likely, the page descriptor does not match the physical page. Ricoh (vendor that supplies AFP viewer) changed their algorithm for the orientation calculation of "Autosize" to reflect how the document is actually expected to print. The environment variable "FixedAutoOrientation=TRUE" returns this algorithm to its previous display, but it will do it for all AFP documents.
The customer also has the choice of setting an actual Paper Size instead of using Autosize and then setting the appropriate Orientation.
Ricoh says this algorithm should have always worked this way. So, there is no "fix" coming..
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The FixedAutoOrientation=TRUE is a setting that you could add to the MISC section of ftdport2.ini file. This can work for the 10.1.0.1 client only. And you'll need to plan for managing the change as you move forward.