I win the award for dumbest cause of the "No such module" error. In my case I build the included framework by hand, and copy it into my project directory. My framework search paths were set correctly, and the framework was added to the project correctly.
When I archived the framework I was building, I used "Show in Finder" to take me to the release folder in derived data. But I didn't noticed that the folder contains only an alias to the framework, not the framework itself. The original framework remained in my derived data directory, so later when I cleared derived data the framework was deleted, but my project didn't know that.
Re-archiving the framework, following the alias to the actual framework, and copying that to my project directory worked.
#import "Social/Social.h"
platform :ios, '10.0'
. That was solution.