Jam wifi speaker volume jumping

[Leebo77]

Hi, I have two Jam Rhythm that are usually grouped however recently they have begun to have issues when the volume is adjusted using the volume buttons on my iPhone, iPad and the slider bar on the Spotify PC app. The volume of each speaker jumps erratically but if use the master slider on the Jam app the volume level on both speakers moves as it should. I connect the speakers using Spotify Connect as it provides a better user experience than airplay (or should do...). Also, I notice that in the Spotify Connect box ‘Connect to a device’ the speaker symbol next to the grouped speakers flashes between 1 or 2 speakers randomly which seems to show that Spotify Connect is somehow having issues with the grouped speakers. Previously the speakers worked perfectly, I’m not really sure why this has happened. I also have issues with spotify pausing and starting randomly....

Grateful for any advice!!!