No idea. I figured it was because you were using one of Medium's weird custom themes and their highlighting color doesn't have enough contrast. Everything in that piece appears to have been highlighted, but on mobile it looked like it had been redacted by the CIA (I hope you could see the screenshot).

And Tony, my website was basically broken for WEEKS (months?) before someone clued me in that they couldn't leave comments. Most people will just wander away without bothering to TELL you. God forbid they should appear CRITICAL rather than just stop reading.