Switch off your router, switch back on after 10-15s. Go to settings in app, click Aurender at the top and ADD Aurender. Exaclty as you did when you first got it. I believe something has changed with your internet/IP address.
That's the most likely root of the problem and good advice. If it remedies the issue, consider going into your router and setting a static IP address for the Aurender. That will resolve the problem for once and for all.