[2020] Dragonfruit patches are randomly going back to a check-health state

We have a fix ready for this. It's just awaiting testing from our release team. Should be out next update if they can fit it in around War's retreat :)

Is this in relation to the Desert amulet? Or something else?

So I checked this during the development of 120 farming and this isn't actually true. The reward states "Cactus patches in the desert will be protected from disease and you'll get double the spines". Spines are only received from cacti and you get 3 without the diary completed and 6 with it completed. Potato cacti do not give spines and are therefore not effected by this buff. They always give 6 fruit no matter if you have the diary completed or not. For this reason the new cacti are also unaffected by the diary reward.