MIDI export problems, lyrics aren't in sync with their notes

I'm running MuseScore Studio 4.4.4 on an Apple M2 Max Studio under macOS Sonoma 14.7.1.

I've got a score with two vocal parts, which (by design) can be sung with a single voice, with both together, or alternating between them. To indicate this on the score, lyrics for the second part would appear in parentheses in the first part, and vice versa; for playback purposes I set the dynamics to ppp for the voice that's silent (and ff for the active one), and since I preferred not to use MS's "oohs" and "aah" I assigned bass clarinet and alto flute as instruments for the two.

I'm now trying out Synthesizer V Studio (https://dreamtonics.com/synthesizerv/) to generate "real" vocals so I can fine-tune the phrasing of the lyrics. To do this I've exported the two vocal parts as MIDI files, which I then import into SynthV, which analyzes the text and melody to generate a more-or-less human sounding result which I can then fine tune.

The first problem I've encountered is that in some (but not all) spots, the lyrics seen for voice 2 are those assigned to voice one (i.e. V1's parenthesized lyrics also appear in V2). This is coming from the MIDI files for voice 2 that MS produced, as I see it when this is the only one imported into SynthV.

In an attempt to fix this I edited the score and explicitly deleted the parenthesized lyrics from each part; the result is that the second voice (in SynthV) only has the correct lyrics in the sections where both voices sing together, while for the other phrases only a single word appears (the last word of that phrase).

So it looks like MuseScore has gotten confused by my edits to the lyrics (e.g. cutting and pasting between the two parts) and isn't connecting the text with the associated notes correctly; since MS has no voice synthesis, this isn't apparent when listening to the playback or in exported audio files.

I haven't (yet) tried deleting all of the lyrics for the second voice and then re-typing them; is there a way to get MuseScore to run a consistency check and (perhaps) fix this?