I also think he is in an UT/OT loop... I also agree 100% with mjohnson!
I used to cap DD's AM nap and it was a disaster! She was cranky all day and woke during the night... had a really hard time settling at BT too.. she would fight her PM nap because she was soooo tired!
I watch her in the AM to see when she is ready for her first nap. It's always between 3 hrs and 4 hrs after getting up. Teething can shorten that time and a good night's rest will increase it... since I don't stare at her all night while she sleeps, I have no clue if she was restless or not... we all have nights that we sleep great and some that we don't. Babies are the same and may not be upset enough to call out, they could just toss and turn like we do and be exhausted in the morning
I only have a few rules... I NEVER wake her from her AM nap. If she needs more than 2 hours, then she gets it. I have actually let her sleep for 2 hrs 45 mins on a couple of occasions

I will wake her from her PM nap to preserve a decent BT if needed. I try to let her sleep at least 45 mins if she battles her PM nap and goes down late... then I will shift BT if I have to.
That said, I would bet your LO needs a much longer span of time before BT. Mine has done 4 hrs since she was 6 months, or she will have trouble settling for the night as well.