Questions about Get users from group api

Jira Development Jira Cloud
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1

I called this rest api.

https://developer.atlassian.com/cloud/jira/platform/rest/v2/api-group-groups/#api-rest-api-2-group-member-get

When randomly change startAt in an asynchronous and call it, duplicate data is returned from different pages.
That doesn’t happen when I call sequentially from page zero.
What’s the reason?