In my own experience, my scroll Id do not always change, especially during the first calls (but calling them again following the "call the last" rule do parse the next scroll). I ran SHA1 on them and even char-to-char comparison to be sure that they were identical and not just alike.
Mooky (Scroll Questions , question 4) and Sujoysett (Do unique/reusable _scroll_ids exist?) seem to have experienced the same situation.
I know the ID is related to shards and/or their state, but I don't know the details. But in my case, it doesn't always change.
Example below:
1)I run the first request, asking for a new scroll context.
Result on the right panel: Some docs and an ID.
- Then I copy/paste the ID in the body of the second request, and execute.
I got some different doc, but same id. (Verified "manually", on https://www.diffnow.com/, and same sha1)
So my questions remain :).