Sorry - my bad for assuming the expression was commonly known.
TL;DR: pronouns in a text exchange are easily confusing.
In conversation, most people aren't actually understanding each sentence. Instead, we're mentally and subconsciously keeping a list of terms that we don't understand - usually pronouns - retroactively applying them as more clues come up to what they are. If you watch as an outsider to a short discussion between two people, you can usually see this in action.
In text, with greater pauses between parts of the exchange (email) and/or out-of-sync replies (IRC/Slack/Hipchat/Discord), it becomes easier for a pronoun to remain unclear. Oddly, instead of saying "I don't know what 'it' is in that sentence" (because we're tracking subconsciously) we tend to just consider what they are saying as unclear in general and mentally skip over it.
If you're communicating via text often, it pays to avoid most pronouns and bypass this sort of problem. Consider the first sentence of this post - had I said "my bad for assuming it was commonly known", you PROBABLY would have followed, because you had sent only one sentence. Had you sent three sentences, "it" would be less clear. Had you written at annoying length as I am, the word "it" would have been quite likely to be unclear.
I'm sure you've had the experience where you send something like "Would it be better to do A? Or does it make more sense to do B?" and the person replies "Yes". Similar cause, though no actual pronoun, just an implied one. Take any email thread with management involved (because everyone top posts and doesn't trim) and you can usually find where people are talking past each other or repeating themselves because pronouns/subjects of sentences weren't clear to the other party.
This post to the contrary, I've found that having SHORT posts but being explicit about subjects and direct objects greatly increases comprehension. I also tend to try and lead with what I need the person to do, or end with a single clear question or statement.
Because communicating by text is a skill, not an automatic perfect ability.