Shortly after Vaan received Emerald's willing cooperation, he focused on sensing his surroundings for the hidden dangers lurking in the background.
However, he quickly realized that while his five senses worked fine, his sixth sense, like the Fourth Dimensional Sense, was greatly suppressed within the secret realm.
In essence, his Fourth Dimensional Sense was like a type of will.
As long as he willed it, he would be able to understand or peruse information about his target, or at least, that had always been the case until now.
However, it became clear to Vaan that there was a greater will within the secret realm that was able to suppress the will of his Fourth Dimensional Sense. As such, he had no choice but to rely on his basic five senses to navigate his way.
Nevertheless, Vaan didn't feel unfortunate about the circumstances. In fact, he felt fortunate for it.