Playback switching between 2 lines.

I am currently editing a 4 part choral piece. The score has the first line sung by the basses and Tenors then the second line is sung by the upper voices, then it splits into 4 parts for the remainder of the song. After uploading the song into Musescore 4, I created extra lines and copied and pasted the correct measures onto the correct lines so that I could create a track for each of the 4 parts. Upon playback of the Soprano line, the Tenor line plays for 2 measures(measure 17 & 18) and then the Soprano line plays for the rest of the song. Is there a better way of creating tracks so that this does not happen? How can I fix this?
Debbie