If a player has left The Nether and walks into an End Portal soon after, the player won't be teleported to The End dimension until they have left the hitbox of the End portal and re-entered as normal.
Steps to reproduce:
Fill the End portal frame
Set up a Nether portal facing the End portal
Go through to The Nether
Go back through to The Overworld
Walk directly into the End portal
That is normal, because if
PortalCooldownis greater than 0, entities cannot teleport in a portal.