It maybe best to reproduce the connection issue(s) seen and then immediately submit a Sonos system diagnostic report from within the Sonos App, note it’s reference and contact/chat with Sonos Support Staff via this LINK and see what the Staff can perhaps suggest to help you to resolve the matter.
I can’t really comment in detail on the Sonos App device volume controls being too small as you’ve not indicated which type of mobile/tablet device you are using, other than in my own use-case they seem to be fine on an iPhone, or iPad here. I’ve attached an animation from an iPhone XR that I use.
