Paul,
I suspect that this is happening because the music notes are not aligned on exact beats or maybe you are in triplet time.
For example...
If you have a look at the triplet at the end of the bar when notation editing mode is operating, the notes and words are aligned.

When I leave the editing mode, though, the notes and words are not aligned.

This is because BIAB is interpreting the display to give the least cluttered musical look to the notes (not the lyrics).
Solution...
Align the syllables manually on the final display.
To do this, it's necessary to do some simple arithmetic. In BIAB, a quarter note has 120 ticks. This means that there are 120 divisions from one quarter note to the next. This is constant.
In triplet time, where each quarter note has three evenly spaced divisions, this means that each position in the triplet has 120/3 = 40 ticks between them.
Since the 'beat position' of a note is always the zero tick value for a note, the three positions for the triplet must be....
(a)
0 ticks(b) 0 + 40 =
40 ticks(c) 40 + 40 =
80 ticks
When looking at the notation mode view after closing the editor, it can be seen the the note that supports the "is" syllable is moved to the 0 tick position.
Thus....
1. Select "Edit Lyrics as Event List". This is under "Edit | Lyrics" in BIAB 2016 and under the "Lyrics" menu in earlier versions of the program.
2. Scroll through to locate the syllable/word.
3. In my example, the word "is" has the music position of 9:4:040. This is saying that the word is located in bar 9, on beat 4 and tick 40.

4. Select the syllable (#1 on the image below), click Edit (#2), set the tick value that's presently set to 40 (#3) to a new value of 0 (zero).

5. This then give the note's musical co-ordinates as 9:4:000 (bar 9, beat 4, tick 0).

6. When viewed in notation mode (and lyric sheet mode), the syllable now aligns with the music display.

Hopefully this helps.
Regards,
Noel
P.S. These "note-length to ticks" values might also be useful
- whole note = 480 ticks
- half note = 240 ticks
- quarter note = 120 ticks
- quarter note triplet = 80 ticks
- eighth note = 60 ticks
- eighth note triplet = 40 ticks
- sixteenth note = 30 ticks
- sixteenth note triplet = 20 ticks