This is not at all unusual. Don't forget, your skin, muscle tissue, and nerves were all cut during surgery. I still have a small patch of numbness/reduced sensation at the old stoma site. It was much more pronounced in the immediate aftermath of surgery; it gradually improved but I still have reduced sensation on and right beside the scar (i.e. the area between the stoma site and my central incision line, and on the stoma scar itself. I would estimate the affected area is less than 1 square inch). That being said, it absolutely does not bother me at all, though if I actually touch the area, it's a bit of a curious sensation as I can't feel light pressure on the skin. It's kind of a novelty thing at this point, though. I am over 6.5 years out from my takedown so I don't expect it will ever change.
Keep in mind that nerves can can a long time to recover, up to 2 years. Most likely some sensation will come back as you continue to heal, but I would not be surprised if you continue to have a small patch of numbness or reduced sensation. As Sharon said, you get accustomed to it over time, to the point that it probably won't bother you.