Hi there, sorry you haven't gotten a reply yet!

Question is is this just teeth, 18 month sleep regression or routine issues?
Boy, that's a loaded question!

I think it could be a little of all three!

It looks like he's on the HSN side, huh? My DS1 was like that and I think somewhere around 18/20mo I had to start capping his nap at 2hr. Also, because he's shortening the nap sometimes on his own and/or waking earlier, I wonder if it might be time to push it out toward 1300.
That being said, it sounds like you think he's a bit OT. I think if you're trying to catch him up, you need to pick either long nap or early bedtime. Trying to do both is likely going to backfire on you a bit as it did the other day.
Ok so last night we tried to force an early bed time after his 0630 wake up . His nap was bad too and he was yawning by half for so we tried putting him down at half five. Tacking on has worked well in he past but It didn't go well with him eventually falling asleep at 1845 by patting. He did stir at 6 am but went back to sleep and woke at 7 ish.
Was the 6:30 wake-up after the 8pm bedtime and 3hr nap? I wonder if he's trying to self-regulate a bit. Can you keep track of your EASY for a few days and we'll see if we can find a pattern?
(((Hugs))), it's not easy when there are so many variables!!