We ran into a functional problem on Edge navigator last week with our application (impossible to scroll around the object on touch devices) so we had to update our plugin from v3.0 to v3.1.8.
This fixed the problem but added another one : our custom html hotspot labels wouldn't display anymore.
It turns out that you apply an overflow: hidden style on the label container, which blocks any attempt to display absolute positioned custom html here.
I tweaked the code to apply overflow: visible to fix this.
Is it be possible for you to add a parameter on the label tag for this value ?