My copy of Ewok Adventure, The (1984) [SF078-1184] has two major drop-outs during the movie, both of which last about a second or less, once on each side. Holding the disc against a lamp revealed a tiny pin-sized hole in the reflective layer, allowing the light come clear through the whole disc, so I assumed that was the reason at first.

But then I looked again and realized there's actually several tiny holes across the disc, I counted about 3-4 in total, but the disc mostly plays fine despite of that. What's up with that?

It means the glue is eating the aluminum - definitely copy off the disk before it gets (slowly) worse.

Since they're small, the player doesn't lose sync, 'tis but a scratch to it.

Always wish I took pics of the discs I had, they were older discovision discs and had major holes eaten away but still played.
Not well but they played.

So you mean the glue literally 'eats'/erases the aluminium to nothing (or at least more realistically some clear reaction by-product) to produce such a visible 'hole' in the disc?
(Transparent aluminium? - just makes me think of the voyage home)

Seems a bit weird that it'd happen in such a specific and precise manner. I'd thought it's something more akin to a manufacturing error.

I have another copy of the same disc already so I'm not concerned about it anyway (except maybe for the ability to sell it down the line) and the funny thing is that despite of that - and it could just be my imagination - this one's a little bit less noisy overall.

That's what I've read and understood, particularly where you'd describe it as a pin-hole. I'd have thought if a hole was forming due to rot the edges would be more irregular (ie: like corrosion).

Thing is unlike a CD where people usually observe these, an LD has two sides so the chances of two lining up on both sides for a hole right through are next to impossible. Perhaps when you hold it up to bright light what you're seeing is the difference between the light being blocked by two layers vs a single layer?

Pinpoint holes are a manufacturing error. Any rot which shows up to the eye on the disc surface will be much more pronounced.