I think detecting or even being aware of register in writing is an also lot harder for some folks than the same thing is in speech, which can lead to problems similar and related to misreading tone. I'd classify that, and difficulty dealing with tone per se in writing, as at least in part also a reading comprehension problem, but ultimately it doesn't much matter the cause when your immediate task is to communicate with the person: your options are to write better for your audience of that person, or, yeah, switch medium to speech.