CP: 1.6.7
MacOS: Catalina 10.15 Beta (19A558d)
After upgrading to Catalina, the Nearby Wifi Network evidence source is greyed out in the Rules tab.

I also see these logs:
...
08:57:08.958 -[EvidenceSourceSetController startEvidenceSource:]
Starting Power evidence source
08:57:08.959 -[EvidenceSourceSetController startEvidenceSource:]
Starting ShellScript evidence source
08:57:08.962 -[WiFiEvidenceSourceCoreWLAN doUpdate]
WiFi interface is active, but is not participating in a network yet (or network SSID is bad)