You could try not cable connecting the Sub and use the dedicated 5Ghz connection?

Actually a non home theatre Sub wouldn’t use a direct 5GHz. In this case it would connect via SonosNet 2.4GHz to the wired One (assuming of course that its ‘WiFi’ isn’t disabled). 

Do I need to change anything in the Sonos app? Or just u plug the cat5?

I’m using the regular sonos sub

Just unplug the Cat5. Assuming you haven’t disabled the ‘WiFi’ (SonosNet) in the product settings for either the One or the Sub it should connect. 

The Sub is the same device either way. I was referring to a Sub which was part of a home theatre setup, or not as in your case.  

Yea.  It still doesn’t work consistently 

What wireless channel does your router broadcast for the 2.4 ghz band? Stick to channels 1,6,or 11

Confirm your Sonosnet broadcast does not also share that same channel.  If it does use a different channel.

also if your Sonos system has ever been connected to your wifi network erase the WiFi network credentials in the Sonos app.  Settings>System>Network>Networks

hope this helps