Hiya, it could be OT behaviour or teething. Have you tried offering meds before sleep or as a dream feed to see of that prevents the wakings?
If this makes no difference, perhaps he is more ready for one nap. My Dd never slept as long as 3 hours in the daytime so for us at this age a nap of 3 hours with a CN would have been too long, but she was reasonably low sleep needs.
Can you APOP naps at all to help him catch up?
Could you try pushing the nap a little later and if you get a long nap go for EBT?