The thing mostly talked about is social isolation and it seems pretty straight forward that going from time in the office to the same time at home reduces social contact.
Losing in-person work relationships at the same time as social relationships is rough. Luckily I get along well with the person I live with, but the lack of ad-hoc social interaction is unsettling.
Once the pandemic is over, of course.
We're already in a loneliness epidemic, WFH will make that 10x worse.
People used to also have extensive social networks outside of work through various religious and social institutions, most of which have withered in the past 20 years or so. This is a huge part of this “loneliness epidemic” you mention. We should rebuild those so that people alternating their work structure isn’t a debilitating blow to their social network. This is particularly important since people change jobs much more rapidly now, which disrupts any social network based on work.