what's going on in this building?

"Represents current apartment configuration, which may not conform to official legal documentation. Purchasers should consult with their legal or architectural professionals to determine legal use parameters."

So its not really really residential, but..

with all the changes in zoning in this city ... why a hard time here?

this is the owner ... really interesting artist and educator
https://chelseacommunitynews.com/2022/06/12/anahid-sofian-celebrates-50-years-of-dance-on-west-15th-street/
https://www.anahidsofianstudio.com/anahid_company.html

Dumbwaiter in the bathroom?

Last CofO (1981, Probably when it co-op'ed) says class A apartments
But unit 9 certainly looks like an office

Bigger concern is they only just last year completed repairs for local law 11 cycle 8 SWARMP repairs which means they are now overdue on cycle 9.
I suspect further repair issues will be "discovered" under cycle 9 requirements