I am using mailpoet widget in the sidebar and it’s missing all the text. It is missing the text above the email form as well as “email” inside the text box. The button says Submit instead of subscribe.
I’m sorry but the issue is really not related to the theme. The styles hiding the form fields are coming from the plugin itself.
Maybe there is some additional plugin or widget configuration needed to display the form correctly? Please check your plugin’s option.
Other thing you can try is to switch to a different theme, to TwentySeventeen, for example, to make sure there is no conflict with the theme. But I presume there is not as from what I can see all the styles are coming from the plugin.