Hi John,
When you saved set 6 , did you leave a blank space in a different spot ie
set6 vs set 6 ?

Something similar happened when I was creating different versions of my 4/4 Ballad style the other day .
They were being saved in order till I left a space in the wrong spot.

May not be the case with with your sets, ( maybe just how it works ) but might be worth checking.