Arduino Yun only connected to the dashboard once, and then no sensor data coming

After I clicked add sensor widget (BMP180), the widget was created and there is no data showing on the dashboard. The top message bar shows “Last known status: 6 minutes ago (Apr 5, 2017, 10:58 am)”. It seems the connection was lost.

I checked http://arduino.local, which said the Yun is still connected to WIFI. The led (WLAN) on Yun was not on though (should it be on?) Led 13 is flashing red.

What should I do now?

Have you tried restarting the Arduino?