Hi and Welcome!
I'm glad to hear the night sleep success story! That must be such a relief to have your son sleeping so well

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The nap training takes longer to work than night training, especially in regard to lengthening the naps. Are you watching the clock and your son's sleepy signs, or just the clock? The times given are a guideline, so make sure he shows sleepy signs, too. Some babies are difficult to read, and it may take time and practice to figure out what is the best time for him.
What is happening with the short naps, is that your son is waking after his first sleep cylce- a sleep cycle is 30-45 minutes in length- when he naturally wakens. Normally this would be a brief waking, and he should return right back to sleep. Instead, he is unable to return to sleep.
There could be varying factors in the reason for short naps- either he is still learning to put himself back to sleep during the day (daytime and nighttime sleep are in different parts of the brain), he is going down when overtired or undertired, or he is losing the pacifier and not able to return back to sleep. If the last reason seems to be the reason he is waking, then you could train without the pacifier. When he's first learning to nap, if it's a hindrance, this is the best time to break the habit. However, many children's sleep is not directly affected by the pacifier, and in that case, it's not a problem.
All in all, it's probably just that he's still learning. Nap training on average takes 2-4 weeks to fully work. I would give it at least another week or two before trying to make any changes. Over time, you will learn more and more about his sleeping patterns, and since this is such a new thing for him and for you, I think you should relax for now and see if things improve.
Hope this helps and if you have any other questions, feel free to ask

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