While playing around in the new snapshot, I noticed that the end portal doesn't work :O
I wanted to explore it, and I created the portal using end frames. It was on superflat, reducedBugInfo gamerule false, and on peaceful, but nothing happened when I put the last eye on. I tried in creative, survival, adventure and nothing works.
Enportalframes have a direction. They should face into the portal. Try to stand in the middle while placing the blocks and it should work properly.