Localization with Loco Translate

I tried do localize just 2 visible strings by using Loco Translate plugin. (Sorry, I do not have time to translate all the strings in the WordPress system). Till now, Loco Translate worked for all plugins, this is the first time it did not work. I generates a template and po/mo, but your plugin does not display the translated strings afterwards. How could I solve this please? Thank you for any help.