Sorry to hear you are having issues with the gpagespeedi.pot file in this plugin. Looking into this more, it seems that shipping translation files with a plugin is not the best path forward anymore. And instead I should look to update this plugin to comply with the guidelines outlined here: https://make.wordpress.org/meta/handbook/tutorials-guides/translations/
I will look to do this in a future update.
In the meantime if you do want to continue using loco translate, they may better be able to pinpoint why it is not working with my plugin. I do not have enough experience with that plugin myself to say.