[Resolved] Translated strings not showing up on frontend

Background of the issue:
I am building a website using a child theme. I've put many strings into the theme (in Dutch), all set for translation. I have indexed the theme and translated the strings. Dutch is the default language, English the second language.

Symptoms:
A few of the translated strings show up, but most do not. Only when I change the strings in the theme to English, then re-index and translate them to Dutch, do they display properly.

Questions:
Do you know what could be going wrong here?