This is expected (working as designed) behavior. When an Omni-Channel user is available but does not manually accept a request, the system temporarily assigns ownership to trace the routing attempt, then reverts to the queue. No configuration change is needed unless you want to auto-accept requests.
To enable auto-acceptance, go to Setup > Presence Configurations > [Your Config] and check 'Automatically Accept Requests'.
See also:
Chat options 'Automatically accept chats' and 'Re-route Decline requests'
https://help.salesforce.com/s/articleView?id=000386589&type=1
000383911

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