Global Queryable Fields vs Collection Queryable Fields

I’m on my dev environment. I needed to add new queryable fields, and I noticed something new or something I had not noticed before: “Collection Queryable Fields”
I read the doc and decided to switch to using “Collection Queryable Fields” since I needed to go trough a client reset anyway.
I defined the “Collection Queryable Fields” for all my collections and I emptied the “Global Queryable Fields”.
But after re-enabling sync, my app did not sync anymore.
I tried many things and decided to add back the “Global Queryable Fields” in addition to the “Collection Queryable Fields” that were set. I stopped and restarted sync and my app now works again.
Is that normal behaviour ?