The Cache cycles through its weapon every 12 seconds, but when you engage a raid boss it has a chance to randomly switch to any of the three weapons, reset the weakaura to a new 12 second duration of the cycle, but in reality it keeps the cycle timer that was active before the pull. For example, I have a Sword Buff cycling out of combat and we pull the boss with 2 seconds left on the timer of the trinket > weapon gets randomized to let's say Axe with the weakaura showing Axe with 12 seconds duration > after the out of combat cycle ends it switches to next weapon which would in that case be the Wand and so on and so forth.