Open attachment 133861 [details] from bug 108343 in current master (after ); save it as XLSX again; open the result in Excel (note that Sheet2!B3 has "Sum - Amount"); refresh the pivot table in Excel.
This removes the text from Sheet2!B3, leaving the cell empty. Also the name of the field in "Values" area of PivotTable Fields sidebar is empty.
This is the regression from the mentioned commit for bug 124651, which was Excel 2016-specific.
Mike Kaganski committed a patch related to this issue.
It has been pushed to "master":
tdf#124881: Provide a non-empty name for pivot table's data field
It will be available in 6.3.0.
The patch should be included in the daily builds available at
https://dev-builds.libreoffice.org/daily/ in the next 24-48 hours. More
information about daily builds can be found at:
Affected users are encouraged to test the fix and report feedback.