- Pause button disabled because no stacking is running at the moment:

- Pause button enabled because a stacking is currently running (and in case of pressing it the stacking will be paused):

- The pause button appears disabled and orange if stacking has been paused:

And in order to resume a previously paused stack you only need to press the run stack button (the one shown below). At that moment Nebulb will detect that the stacking was already started previously and will continue where it was going (it will not run it again from the beginning).