https://www.youtube.com/watch?v=U1Edf2-zkUs
He has taken a step back since early November after brilliant start. understandable at such young age and tough opponents they had to play
Hopefully he will step up again
He is young, his form is hot and cold.
But also, another factor: every player has some amount of matches of "a free ride" while opponents are not yet familiar with your abilities, when they are not marking you strictly and they don't know your typical tricks.
In short:
1. you have a period where you are somewhat unknown, opponents don't mark you too hard and they don't know your tricks
2. after some time, opponents realize who you are, you are marked way more heavily, you get way less space, you have to beat more and more defenders to get into chances, and opponents learned how to defend against your typical tricks
3. phase 3 for every young player is to learn how to play against defenders who mark you more heavily, and to raise your game to the next level:
-- with more variety in your play, new solutions, surprises etc
If Halil will overcome this new obstacle, he will eventually face new obstacles and will need to improve his game more and more (every year).
Best players over time overcome a majority of obstacles.
While some others get stuck somewhere in the middle and end in Stoke, Levante and similar.
So, Halil now needs to make a next step in his development.
Raise his game further.