I've gone weeks, literally - weeks, without seeing some fish after introducing them. The one that blew me away was my Red Sea Sailfin tang when I first got him. How can you lose a tang in a tank?? But he found a pretty good hiding spot. Couple weeks before he was comfortable swimming around.
Same with fairy wrasses -- man, I never saw my lubbock's wrasse for a solid MONTH. I thought he was a goner for sure, I was sooooooooo depressed, like you wouldn't believe. One day I saw the loser's face poking out. It took him several months to get used to the idea of people looking in the tank. I lost him in an anemone incident.
My newest fish is a potter's angel I got from Willito about 6 weeks ago, and she was pretty shy for a solid 2-3 weeks. Again, could see no trace of her. But she's out all the time now.
Take it as a compliment, you've obviously done aquascaping well enough to give them a good choice of hiding spots.
Hopefully that's all it is. Good luck.