So DS has never been good at going to bed but we had about a month stretch where we could tuck him in (he's in a twin bed, no rails) and tell him it was time to go to sleep and he just would! It was great! As much as I enjoyed it, I told myself that it was likely a good phase, as everything seems to be.
Well for about a week, he was getting out of bed repeatedly and we'd just continue to put him back until he gave up. The last week or so, we're doing the same thing, and now he's staying in bed, but he's spending an hour (on and off) screaming before going to sleep!
He's still taking a 2 hour nap in the afternoon, usually 12-2ish. My only thought is maybe he doesn't need a nap and isn't tired at bedtime? Or maybe, like everything else, this is a phase that will eventually resolve itself?