That’s a pretty good indication of some sort of wifi interference , causing delays between your controller device and the Sonos speakers. There is also the minor possibility of duplicate IP addresses. If the suggested changes in the linked FAQ don’t provide some relief, try unplugging all your Sonos devices from power, then reboot your router. Once the router has recovered, plug your Sonos devices back in. 

I have exactly the same challenges, the App is pretty much unusable as it is so slow/lags
Yesterday I turned off "Use IR & IR signal light" in the App.
Instantly the App worked as it once did, I could turn the volume up and down without the slightest delay.
The downside is that my Apple TV remote control does not work on the sound now, I think I need to investigate this a bit more..

Which SONOS soundbar are you using?

Had the same issue. Was able to fix it by removing unused Wifi networks in the “Manage Network” section of the settings.  

I have endured the same issue for years. Router IP addresses for each Sonos component are static. Stream from NAS or Spotify same issue. Hit Play from physical device and no lag, just up to 30s for app to find devices and to change songs, etc.

It shouldn’t be that way. 

I would recommend that you submit a system diagnostic within 10 minutes of experiencing this problem, and call Sonos Support to discuss it.

There may be information included in the diagnostic that will help Sonos pinpoint the issue and help you find a solution.

When you speak directly to the phone folks, they have tools at their disposal that will allow them to give you advice specific to your network and Sonos system.

Thanks, Bruce. That’s something I’ve not done but will get on to.