I’m pretty sure every creator has had this happened at least once
I can’t say for sure but when I have an idea for a chapter even a future one , I write the basics down on my notepad app.
For example Azalhana is introduced and explained is a random thought that popped in my head before going to bed. By writing it down I can kinda focus on this one sentence and think about how I want to lead up to this topic. After brainstorming I write a couple of sentences, even writing one is great,and bam as soon I know it I have a good paragraph down.
Then I take a break to recharge my mind and reread the last couple of chapters just to make sure that the idea I wrote flows through nicely.
I don’t know if this will work for everyone but it has helped me a lot.