PREP_EXTENSION/EHP_INCLUSION error in S4/HANA 1610 update

[ps0907]

We are upgrading from S4/HANA 1511 on-premise to 1610 and we receive an error in PREP_EXTENSION/EHP_INCLUSION :

Severe error(s) occurred in phase PREP_EXTENSION/EHP_INCLUSION!

Last error code set: Stack file is invalid: component 'UIAPFI70' (stack release = source release, but KEEP not allowed) If you put new packages in the download directory, use option 'init' to upload them Trouble Ticket Generation A trouble ticket and an archive with all relevant log files have been generated.
Trouble ticket: "E:\SUM18\SUM\abap\log\SAPup_troubleticket.log"
Log archive: "E:\SUM18\SUM\abap\log\SAPup_troubleticket_logs.sar"
Repeat phase PREP_EXTENSION/EHP_INCLUSION to continue at the point it stoppedInitialize phase PREP_EXTENSION/EHP_INCLUSION to restart it from the beginning

The 1511 system is currently at UIAPFI70 SP01. According to the XML generated in Maintenance Planner, this component is being retained and updated to SP02. There is no prompt during SUM to select 'Keep' or 'Upgrade' for this component so the KEEP decision is occurring internally. Regenerating another maintenance transaction results in the same stack components selected.

We have tried resetting the upgrade and repeating with the latest version of SUM (19), but the same error occurs.

We have opened an incident in Service Marketplace but there has been no activity, still in 'Sent to SAP' status. Has anyone else encountered this error?

Thanks in advance.

[ps0907]

SAP support instructed us to reset the upgrade and rebuild the stack.xml to include an upgrade to UIAPFI70 400 along with the 1610 upgrade. Once this was done, the EHP_INCLUSION phase completed and the upgrade was successfully completed.