2671937 - WDA: "Back-end session was closed after timeout" during Excel file download inside Portal in IE11

After downloading an Excel file in a Web Dynpro ABAP application inside Portal on IE11, when interacting with the application again, the following message is raised:

"Back-end session was closed after timeout. Your session has expired."

Observation: the issue does not happen outside of Portal, or in other browsers. It also does not happen when downloading other file extensions, only Excel spreadsheets.

• Web Dynpro for ABAP
• Enterprise Portal
• Internet Explorer 11
• SAP NetWeaver 7.5
• SAP NetWeaver Application Server 7.51 for SAP S/4HANA 1610 (SAP_UI 7.51)
• SAP NetWeaver Application Server for ABAP 7.52 for SAP S/4HANA (SAP_UI 7.52)
• ABAP PLATFORM 1809 - Application Server ABAP (SAP_UI 7.53)

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