Xenia or Kenya? Seemed like you have crossed the two different coral names
Either way, have you checked the sandbed around the rock structures? Both types of coral tend to shrivel and slime quite easily so it could have just slipped loose and taken by the current. Any crabs in the system? Hermits are also attracted to the slime given off from newly introduced corals and could have jarred it loose. None of the fish you have are listed as corralivores.