We had this when we first went to v10. It was the timeout in Landmark - it was set to 1 hour and it defaulted over to S3. The buyers tend to have inbasket open as one of their screens so when one timed out they all did. I don't know what my IT did to fix this though.

I think our situation is different since this is not related to a common in basket.  I opened a ticket with Infor and received the following response:

 

I did some research and found that this had been reported as a defect before, but they did not revert the functionality. Here is the explanation:

This was discussed with the teams involved in the investigation of this case which wrapped up today.

Here are our clarifications to this issue's outstanding items:
- The modal dialog login page was removed because the browser vendors themselves dropped the support for modal dialogs due to functionality issues and vulnerability risks (see references.docx for sources)

- In order for a user to be redirected back to the form where the session time out is experienced upon re-logging back in, there will need to be an intrusive enhancement on Portal

 

In other words, it appears this functionality was removed due to vulnerability risks.  Bummer....