By M. E. Gewand, “The Lindelöf degree of scattered spaces and their products,” Journal of the Australian Mathematical Society (Series A) 37 (1984), 98–105, we have:
Theorem. Every Lindelöf scattered $T_3$ space where each point is $G_\delta$ must satisfy $|X|<\omega$.
I think this is a typo and should be $|X|\leq\omega$: a converging sequence is Lindelöf (in fact compact), scattered, with each point $G_\delta$, but is (countably) infinite.
We can see also the following:
Theorem. Every Lindelöf locally countable space must satisfy $|X|\leq\omega$.
Proof. Cover the space with countable open sets, then take a countable subcover. The union is countable and contains the space.
Does the following hold, providing a proof of Gewand's result above?
Conjecture. Every scattered space where each point is $G_\delta$ must be locally countable.