I think the first issue is likely to be OT - perhaps the nap is too early in the day, perhaps it is because daycare is too stimulating, but it seems like something has thrown him off and now that he is waking so early and refusing to nap, OT will definitely be a problem.
Now I know this wouldn't work for my 2-yo, but it might have worked for dd1 if she was waking early, so have you tried 2 naps? Maybe just 15-20 mins in the morning and then nap 2 slightly later in the day? Like I said, I know I wouldn't be able to get dd2 to do this, so it might be a pointless suggestion.
I think that you might have to tackle the EWs with wiwo - if he is waking habitually after 10h, it seems like he needs to be 'reset' so that his expectation is that if he wakes at that point he goes back to sleep. We solved my dd2's EWs with a light on a timer (he's definitely old enough to understand the concept) - she used to wake between 5 and 5.30 and now she wakes sometime between 6 and 6.30 but we don't hear her until after 6.30 when the light comes on. It took about 3 days for her to get the idea - those days we just went in and explained that it was still sleeping time and she had to wait for the light - and after that she would point at the light every morning when I went to get her up.
I also think that teeth could still be a part of it (unless you know they have all come through) - they take ages to come through and can cause havoc all the while. Have you noticed any difference if you give meds before nap and bedtime?
Finally, I would resist the temptation to let him sleep more than 2h during the day to catch up - no matter how tired he is, a long nap is just going to mess with his nighttime sleep. It will take a few days, but he will catch up his sleep if he gets back on a consistent routine where he is getting the right amount of sleep in 24h.