Agreed. Same issue here, on iPad & iPhone. 
Sonos app release 14.18.1

If I remember correctly, previously you could touch the volume slider dot first then you could make your adjustment. Now, as you mentioned, upon initial touch of the volume slider dot it jumps to a lower volume. Also affects any grouped speakers. 
 

Please fix ASAP. 

Yes..same issue here. In testing it, I’m making sure that when I touch the slider dot I’m not moving in either direction and still….the volume jumps to the left. Don’t know why they had to change it. Was perfect before.  Please get this resolved Sonos.

Hi @grunr

Welcome to the Sonos Community!

Please ensure you have no other apps open (music apps in particular, like Spotify) and try again - do you get the same results? If so, please try rebooting your iPhone and try again. If you still get the same behaviour, please then submit a support diagnostic and report the number given here. Please also let me know which room you were adjusting. Thanks.

I hope this helps.

here is diagnostic submit code.  1420820993

I submitted the diagnostic.  btw it is happening on my ipad as well. and i see there is a post about volume slider problem on desktop software as well.

It may be of assistance if you’d take a screen record of this behavior as well.

https://support.apple.com/en-us/HT207935

Hi @grunr 

I’ve received an update on this - we are aware of an issue whereby the volume can adjust by several steps too many when tapping on the volume slider on iOS devices. We are investigating the issue and do not have a timeline to share.

In an unrelated coincidence, there is also an issue with group volume control on the Windows controller app.

Hi Corry P. The issues are more extensive than you have cited, so I thought I had better chime in as I have been noticing odd volume behaviour for several weeks.

In a post I made in the Facebook “Sonos Users Group” I added a video that shows the odd behaviour (I could not upload the video here). Every time you see the volume snap back in the video, that is Sonos doing it by itself. Also note that the iPad volume bar keep popping up at the top, and that is despite Hardware Volume Control being turned off on all my devices. The last interesting thing is that this behaviour is also happening with touch buttons on some of my speakers - tap up or down, and the volume often heads back to where it was before the first touch. Needs persistent taps to get the volume to stick.

@arcadelt,

If I try to follow your link to the Facebook video - I just see this message (see attached)?

Are you a member of that group Ken?

No, sorry I don’t use Facebook at all - I just assumed the link was publicly available, particularly as the message just mentioned the ‘video is no longer available’, as though it had been taken down/removed.

Ken, I tried to link to it more publicly through my OneDrive account, but that wasn’t allowed here either. I’m hope those that want to view the video have access to that group or could advise me how to post the video here. Suffice to say, the volume setting situation is not good for a number of people.

Ah that’s okay - no worries, I just thought there might have been an error in the linking to the video. Thanks anyway.

Looks OK from my end: