Lex?
The sensation was not originating from some specific person or place. There was just a hint of it mixed in with the general environment. It was like an unexpected, unpleasant smell in an otherwise nice place.
Lex had become more sensitive to such things in the last few years while he tried to hone his powers and abilities. Since he could read people's emotions really well, it was just one step forward to sense the influence their thoughts and emotions had on their surroundings.
In summary, it was a cultivator version of a vibe check. Some people, while putting up a front of being kind and amicable, were harboring dark thoughts relating to the Saintess Yildrim. It wasn't too surprising since she kept a firm check on anyone who wanted to do anything illegal.