Are you on iOS or Android ?
I seem to recall that Runway HD does not yet support bearingless trafficon Android, I could be wrong.
Also check that Bearing less targets are enabled in the navigation software.
Please check your Mode C/S settings on the PilotAware configure page, I recommend the following settings initially :-
Mode-C/S Separation - 1000ft
Mode-C/S Detect - Short Range
Mode-C/S Select - Mode-CS+Filter(Beta)
then go to the traffic page and confirm you see any traffic which is :-
Mode-S
CS---
or Mode-C
C----
Audio/Visual warnings are only generated for Mode-C/S when specific signal strengths are met. (SIG column)
These are determined by the 'Mode-C/S Detect'
Thx
Lee