It sounds like you're in a bit of an overtired cycle at the moment - (((hugs))), the 2-1 transition can get pretty messy
A few options for you to think about - you could try a catch-up day where you just put him down when he looks tired, hope for two naps and a better WU tomorrow. It's a risky strategy for LOs who are refusing the pm nap but may work if he is really tired. Option two would be put him down for a very tiny morning CN. Then a short A time, followed by another nap. This has worked pretty well for both of my LOs during this transition. As an example something that has worked here is roughly WU 5.30, nap 9.30-9.45 (15 mins) then nap 11.45- whenever. Then on a reasonable WU day you push through to one nap. Option three is set nap and (early) bedtime and ride it out for a while. Say 11.30 and 6/6.30pm. Option four is to push your one nap later by 15 mins every few days until it is closer to 12 (for a 7-7) day and make good use of EBT until nap lengthens.
Just as an idea we have now set our nap at 11.45 (got to that in 15 min increments starting at 10.30ish) as DS will be having a set nap then at nursery (starting this week). We pushed through to 6pm bedtime even on a short nap, although did offer a pm CN on some days (almost always refused). WU did eventually start to improve a bit but is still a bit prone to EWs. If OT is clearly starting to build and/or an EW I've done the 15 min CN as above just to get him through to set naptime as that's the time I want his body to be used to resting, or if that's refused then pull nap earlier but only by 15 mins or so. Our BT right now is around 6/6.15pm, but hoping to get that a bit later as he gets more used to it. Morning WU has varied from around 5.30 to 6.45, but I'm leaving him in bed until around 6.30/45 anyway as he's just dozing/chewing his lovey/chattering. So not entirely sure when his WU is
Is that any help?