After extracting parts like normal from a score, chunks of measures go missing. And it's not necessarily the same measures in each part, i.e 77, 78, 78, 92,93, 94.
It would help to know which version of Finale you are using. Have you attempted to use the Linked Parts feature? Extracting parts is from much older versions of Finale.
Ted Boliske
Mac OS 10.12, 10.14, 10.15, Win7, Win10 VDL2.5.5, Finale 2010-14.5, Finale 25-27 Kontakt 4-6, various other soft synths