To an and others:
I googled “Is San Diego gaining or losing population?”
It reported a decline of 11,183 from the previous year, as of May, this year, and this was reported in the SDUT, LA Times, VOSD, etc. in May and March of this year. an quoted UN statistics which seemed to be a projection of previous years’ trends, when population was clearly growing. You can trust in UN estimates if you want–I trust local sources.
As sdr suggests, we don’t know if this is COVID inspired and thus temporary. Speaking of COVID, the work-from-home trend may be prompting the exodus from CA to less expensive locales. We also don’t know if it includes illegals or not (footnote: one source said SD had the third highest number of homeless of US cities).
What is clear is that San Diego’s competing cities in Arizona, Nevada, Texas, etc. are growing rapidly, as are their RE values. People (and companies) are voting with their feet.