Dragging the 'Amplitude' handle works as expected but dragging 'Frequency' afterwards moves *both* of them together. Happens with 'Phase' and 'Offset' as well. Does not happen when I click on the base left or right of the .handle. You can even click anywhere in the .widget-box below the sliders to move them. It looks like chrome associates .bk-noUi-handle elements with the .bk-widget-box instead of their individual .bk-widget but only after they've been selected once.
I can't reproduce any problem on current Chrome 63. Chrome 51 is going on two years old, unfortunately due to lack of resources its unlikely we can investigate an issue like this on such an old version. If you happen to have a small fix that can be demonstrated to work on current browsers, we'd be happy to consider a contribution.
Dragging the 'Amplitude' handle works as expected but dragging 'Frequency' afterwards moves *both* of them together. Happens with 'Phase' and 'Offset' as well. Does not happen when I click on the base left or right of the .handle. You can even click anywhere in the .widget-box below the sliders to move them. It looks like chrome associates .bk-noUi-handle elements with the .bk-widget-box instead of their individual .bk-widget but only after they've been selected once.
Upgrading to version 11 is something we could try easily enough. If things look good and a PR is merged, we can publish a dev build that would be easy for you to test. Can you make a GH issue to request updating the nouislider version?