Created tooltips on labels for checkboxes such that the tooltip displayed over the checkboxes. After mouseleave, the tooltip hides, however the functional clickable area in which the tooltip had resided was no longer interactable with the mouse.
Further inspection showed the tooltip remained in the DOM in it's location with opacity 0 and z-index: 0;
A quick CSS hack to fix the issue was possible.
z-index: -999 !important;