Re:The Decline and Fall of the Latin Neuter
by stevula on Thursday March 25, 2021 @12:29AM
(#26576608)
The etymology you linked actually says something different:
> From a Vulgar Latin *lo, *illu. Masculine pronoun from Latin illum, singular masculine accusative of ille. Neuter article and pronoun form from Latin illud, neuter of ille.
https://en.wiktionary.org/wiki/lo#Spanish
That means some uses of "lo" are derived from masculine ille while others are indeed from neuter illud. To answer your phonological uncertainty, the entry shows derivation from illud > *illu > lo.
> From a Vulgar Latin *lo, *illu. Masculine pronoun from Latin illum, singular masculine accusative of ille. Neuter article and pronoun form from Latin illud, neuter of ille. https://en.wiktionary.org/wiki/lo#Spanish
That means some uses of "lo" are derived from masculine ille while others are indeed from neuter illud. To answer your phonological uncertainty, the entry shows derivation from illud > *illu > lo.