I would stick at it. Routine changes can and often do throw up odd disturbances whilst LO settles into it. Sorry you had a bad night though, I hope tonight is better for you all.
Prior to the EW and the 10.30am nap was his nap 11.45 or something else? Just wondering if you have reached the previous routine nap time yet or not.
One other thing, now that he's had a few NWs rather han just the EW I looked again at your LOs age. There is often a language leap at around 21 months, I wonder if he may be close to this? It can of course come early for some LOs. The language leaps for us (and threads I've seen) cause huge night disturbance, shockingly so. I wonder if you remember going through it with your older DD?
But like I said, might not be the leap yet, might be any number of things, a tooth moving, a cold on its way, settling into the change in routine...