Export timings vary a lot on similar sets of data

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Hi,

I'm using the Workforce module with 3 additional custom dimension.

I was exporting data on 2 different sets of Level-0 entities and I made sure empty blocks were cleared beforehand.

It was very surprising to see the first set (Load Id 525), which has some more entity members and more number of records, just took 13 seconds to export.

Another set (Load Id 525), which has much fewer records, took almost 2 hours!!

I did some data profiling and found that 2 sets have similar data pattern. It's not one set has data all across a lot of sparse members. Both set have of data are quite limited in only a few sparse members.