"“When it comes to idols, there will be no consistency,” Probst told us out in Fiji at the start of filming. “Usually there’s a theme. You have to find them in a certain way or work a certain amount of effort to get it. Not this time. One might drop in your lap, one might be at Tribal, one might be at the bottom of the well, one might be at a challenge."
Mattiam I think it was because Tai was looking for the idol after the challenge...while Troyzan was looking before the challenge. They might switch them out depending on the time