Hi 🙋♂️,
I'm sorry to see that, I had similar issues in my reports, but I had different reasons than what I suspect you have.
With EC & pH values being fine, it probably has to do with some other environmental influence, like too high light intensity... that was the case for me back then, but I don't suspect that for you.
This error pattern also occurs when the roots have a problem, for example caused by waterlogging. I suspect that more for you, as the soil couldn't dry out properly due to the sand.
Another possible factor is the humidity in general, but I don't think that's it.
I hope this helps & I hope she pulls through again!
Good luck moving forward 👊🤞🏽👍