Another day, another plant woe...

I thought dragon plants were indestructible but mine is looking peakier by the day. Its leaves are turning brown, and I don’t understand why - I water it when the moisture sensor tells me I need to (when it’s dry down to maybe a cm or two), and it’s near a big south-facing window.

What am I doing wrong?

(Houzz is not letting me post a photo right now for some reason but I will try again in a bit)