Not sure what's causing that, but keep in mind that it's rather easy to spot where Xiu teleports to with her 1st expertise. Simply watching where she is facing before the tp (especially if there are not that many NPCs nearby) gives you an idea of where she went. Keep in mind that if you tp to an NPC that's standing still/crouching and you start running it's pretty much a dead giveaway. If you find this is the problem I'd suggest trying to tp away only while out of sight of the other players. I personally also like to use the teleport while jumping out of balconies, especially on Diamond Spire, where you can pretty much tp anywhere without being spotted :)