Essbase data load fails with unknown members error 1003000 after EPM 11.2.12 upgrade

We have upgraded our 11.2.3 EPM system to 11.2.8 and then to 11.2.12 (both were in-place upgrades). Now we are trying to syncup the development system with production in terms of data and metadata before starting with the 11.2.15 upgrade (in-place). The dev environment does not have much space to hold all of production data and so we exported a subset (one scenario and a month of data) from prod.

We get the Essbase error 1003000 while trying to load this data file whereas there are no unknown members as such. The error talks about the very first line in the file that has the column headers (Period dimension members) such as Jan, Feb, etc… These are basic members that any database would have and the application has all these members. The member names are similar between the export file and the outline (this is a planning application). The error message did not include the member BegBalance which is also in the column header but didn't have an alias name.