If you click-assign identical lyrics to multiple parts, all sorts of jumping around may occur if anything changes in any of the parts.

You might want to copy the lyrics from one singer's Edit window (Verse) into a separate window (Chorus or Section) and assign the second singer's lyrics from there. (Just remember where the lyrics are if you need to adjust one of the baselines.)

Also, assigning lyrics at random times can lead to later problems. I admit, I do both myself for convenience, but I am not surprised (and kick myself--figuratively speaking) when problems crop up.

(I expect that in something as large as an opera, this must be particularly maddening.)

The prayer of all Finale users who do large scores with lyrics. Someday, let the Lyric tool work as advertised. Admittedly, that used to be the prayer of all Finale users who had to deal with lyrics, even lead sheets.

The Lyric Tool has seen so much improvement over the decades but, on larger scores, I still enter mine directly (as time consuming as that is) instead of using the LT.

if the MM gurus have any suggestions for making this work as smoothly as possible, I'd like to see them, too.