Did you check if destination (WAP IP is 169.254.1.1) has a return route for 192.168.20.1 pointing to SRX?
Run "show security flow session destination-prefix 169.254.1.1 protocol icmp" after running a Ping and check if you see a valid session.
If you see a session with packets going out and nothing in return then its a route issue on destination
If you dont see a session itself, then run a flow traceoptions.