I think the Leibnizian cosmological argument is deductively invalid.
a1- It is logically possible that God did not have a sufficient reason for creating the universe.
a2- It is logically possible that the principle of sufficient reason is violated in some cases. (from a1)
∴ Then it is not logically necessary to seek a sufficient reason for the primordial physical state. (from a1, a2)
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The only way to invalidate premise a1 is to show that it is logically contradictory for God to create a universe without a sufficient reason. However, this leads to strange consequences (such as modal collapse).
The only way to invalidate premise a2 is to necessarily show that the principle of sufficient reason is universal. To do this, it is necessary to object to premise a1.
The another way to invalidate conclusion is to show that the principle of weak sufficient reason is necessary. This principle arose as a result of narrowing the main principle. However, it is not necessary to accept this principle.