If you temporarily have additional lyrics to a voice you can keep the lyrics context alive with the following construct. Unless you do this, a further temporary lyrics context would create a separate line (if it happens on the same system of music).
The solution is to create one or more named lyrics context(s) with
\new Lyrics = "lyr1"
\new Lyrics = "lyr2"
…
before they are filled with the lyrics text.
It is noteable that the definition of the contexts must use \new … while later references must use \context …