When an individual takes a DNA test from two different companies, the results may somewhat change despite testing the same DNA for several reasons.
First, each company may use a different population reference panel and may also partition it differently into specific populations.
Second, each company uses a different computational pipeline.
And third, different companies may use a different technology to capture the genetic variation of an individual. At MyHeritage we currently use an array covering roughly 700,000 markers spread across the genome.
This last factor also explains why if you previously uploaded your raw DNA tested by another company to the MyHeritage site, the results might have differed compared to testing your DNA with the MyHeritage test - the somewhat different coverage of SNPs across chip arrays used by different companies can lead to small differences in the results even though we use the same computational pipeline and reference panel in both cases.