I might be way off here, but here's my thinking.
Yes. Your LO is in an OT cycle, but you are putting him down too early for the first nap.
My LO has always been on the low end of A time for the first nap. But even he was taking a later nap by 13 months, and we too struggle(d) with short nights and very wonky naps at that age.
Here's what I would do if I were in your place, for what it's worth
Do what Becky and Michelle both suggested. Make that first nap later. But, I would let him sleep as long as he wants/will. We went back and forth between a long am nap, short pm nap --and-- a short am nap and long pm nap for a long time here.
The short am nap is not working for you. (or you haven't tried it like suggest, I agree 4.5 hours is WAY too long. There were days after a 30 min nap that my LO wanted to go back to bed after 2 hours. 3 hours is the norm that works best for most people.
If you truly feel that your LO will fight that PM nap on even 30 min after a shorter A time like Michelle and Becky suggest then I would strongly, strongly recommend trying the long AM nap. If he refuses the PM nap then give him a super early bedtime again.
If you are currently doing 3.5 hours A time, then maybe try 3.75. Add 15 min to what ever A time you are currently doing. Keep doing this until you find an A time that gives you at least a good solid 1.5 hour nap.
When we first switched to one nap 4.75-5 hours worked best.
I remember our first very successful nap day started at 10.45.
Most days at 22 months my LO still wants to go down at 11. I'm currently working on that.
I found that if I put him down at 12 he slept 1h10m and woke screaming and would not go back to sleep.
If I put him down at 11 he slept 3 hours. That's hard to beat. So it's just a matter of finding out what works best for your LO.
Really good advice I received when going through the transition was try putting him down at 3.5-4 what ever is your normal A time. If he fights you do not fight him for a long time. Such as 1.5 hours. After 30 min or so get him up. Give him an early lunch maybe a little low key A time and then put him back down again (probably for his only nap of the day) let him sleep as long as he wants, do an early bedtime. We did have quite a few of these days, and they were hard. But this is just a phase and you will see light at the end of the tunnel at some point. For a good number of spirited babies it seems to be about 15 months of age
I think for a day I would even try staying in the room, maybe napping with him to see if you can get him past that wake up period. If he's teething you can deal with the sleep training later.