What are the full set of responsibilities of the team member? Are they being tied to previous projects? Is there something that is getting in their way? Is there a culture clash?

Also, understand that the new person is learning the context and team culture, and will take some time to get up to speed. How long have they been on the team? How long have you been on the team? The other team members?

There is a lot of context to consider. We can make a lot of assumptions based on our own experiences, but may end up sending you astray.