Struggling with localisation gfx.getLocalizedText("key")

I’m using gfx.getLocalizedText("key") for all strings in my game, but sometimes find that strings default to the key value and not the value in the en.strings file and cant see any obvious issues. is there knwon things that trip up the parser?

e.g.
"showtimeron" = "LEVEL TIMERS ON"
"acontinue" = "to continue A"