During a current sprint, a team member asks permission from the scrum master to investigate...

Discourage the team member from deviating from the plan and document the request during the retrospective

Encourage the team member to research the issue and present the findings during the retrospective

Discourage the team member from using experimentation/spikes unless it is fully developed and accounts for a variety of use cases

Encourage the team member to use experimentation/spikes for continuous improvement and help the team understand why it is important.