Which SONOS models are in your system? Describe your network for us.

You might power down all Sonos, reboot your router and power the Sonos back up to see if that clears the problem for now.

Long term fixes should be possible, start by answering the post above.

I tried powering down everything for an hour  I got everything back on line except 4 SL ones and the mini sub. 
the system can see the units but will not add them to the system. Router was reset numerous times as well

You have not given us enough information about your system and network. I think that it will be best if you work with SONOS support.

I have Sonos arc, sub3, and for surrounds Sl systems, using it for about 9months, I’m facing the issue of volume automatically fluctuating repeatedly while watching any content or listening to the music, how to resolve this issue ?