Enderdragon did not spawn

I had made a new world to explore the new snapshot in, and after a while of exploring stuff in the overworld in peaceful mode went to find the nearest end portal (creative mode, using ender eyes to locate it) then filled it in with eyes like normal and went in. I spawned in the end as expected but realised there was no boss bar, and I flew around the island to see if I could find the dragon, but no luck. I switched away from peaceful and endermen started spawning, but still no dragon. The exit portal was not completed.