census block group has zero occupied housing units but positive population

Hello,

I'm using ACS 2015-2019 five-year estimates for census block groups in LA county. I notice that there are census block groups that have zero occupied housing units but positive population. I was wondering how is that possible. If there are zero occupied housing units, where do these population live?

The following census block groups have large population but zero occupied housing units. 060372653011 (population: 11977), 060379202001 (population: 5393), 060379010031 (population: 4895), 060375746011 (population: 2276). I saw on the map that 060372653011 basically covers UCLA. I cannot tell what regions the other census block groups are at, but some of them seem to be in the canyon/mountain areas.

I was wondering whether anyone has any idea why census block groups that have zero occupied housing units could have positive population. Thank you.