The appearance of the fa-minus-circle and fa-plus-circle icons in Font APEX is inconsistent with respect to that of the previous Font Awesome rendering, and with the class naming conventions used by both font libraries.
In Font Awesome, the fa-minus-circle class generates an inverse minus sign inside a solid circle:
There is no corresponding outline icon, but if there was, it's clear that by convention and correspondence with the equivalent minus-square classes that the class name would be fa-minus-circle-o.
In Font APEX, the fa-minus-circle class generates a minus sign inside an outlined circle, and there is no corresponding solid icon:
This is in contrast to the Font APEX fa-times-circle classes, where both solid and outline icons are rendered as expected using historically and internally consistent naming conventions:
This causes problems in upgraded applications as (1) the rendering of these plus/minus icons is now inconsistent with that of other circular icons such as times and check marks; and (2) there is no solid version of the icon available at all.