I just noticed that the site can not be indexed by google due to the <meta data-rh="true" name="robots" content="noindex,follow">which is coming from Head Tags API.
Do you have a SEO plugin such as Yoast or All-in-one-SEO installed? If so how is it configured generally? How is it configured for individual pages/posts?
So the meta robots instruction varies depending on which page you land on. If you have a SEO plugin please check the settings for each page. The head-tags plugin is zero-config apart from state.frontity.url and state.source.api in frontity.settings.js which are already set correctly according the repo that you provided.