What product do you have it bonded to? 
 

Have you tried adjusting the bass settings and/or the Sub level in settings? 
 

Try depowering your Sonos devices and then restarting them. 

Your profile data let me assume that the sub mini is bonded to a Beam2 within a surround setup. Which way the Beam is connected to your network? Wireless or via lan cable to the router?

If you use it via lan, make sure the Beams wifi module isn‘t disabled anyway.