When people in my family have died (father, mother, brother), I sometimes tended to have delayed reactions due to my autism and trauma. It took a while, maybe weeks, months, even years for feelings to come up and be felt in all the complexity that involves a parent or sibling.
I didn't have the best relationship with my mother (and brother). It took awhile in her case for all the emotions to arise. It hit me again, years later when I found myself grieving her death as if my emotions had just surfaced, with new understanding of all that happened.
Autistic grief can be different. Delayed, complex. But no less impactful in my case. I'm still learning new things about my family and my relationships with them.