Relatively often "I can't parse this" is still about the grammar, more specifically when it's not clear what words belong together. As an example from the artic

Relatively often "I can't parse this" is still about the grammar, more specifically when it's not clear what words belong together. As an example from the article, "certified community behavioral health clinic" is a single token, but if you don't know the term, you won't parse it correctly. In other cases a sentence might contain technical terms as adjectives/adverbs where it's not clear which word they modify. Or possibly the content is just so confusing that you begin to doubt you parsed everything correctly...