The stamina is always dropping if the spy is cloaked. The cloak drains stamina at a set rate. When you sprint/roll, that action takes its normal amount of stamina. The endurance award is an auto-regeneration of the unit's stamina. The edurance award regenerates the stamina faster than the cloak uses it. If you are moving around when cloaked and you have the award, your stamina stays the same (it is decreasing and increasing at the same rate). When you stop moving, it increases, but when you don't have the award and are cloaked, it is always decreasing.
Test: Be a Bothan Spy in an online game (so you don't have any awards starting out) and when you respawn, cloak yourself. Don't move, just cloak. Your stamina will go down.
(I may not agree with thoughts posted under this name)
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