Unable to remove a member from a team: RemoveMemberFromPrivateChannelFailed

I'm trying to remove a number of members from a team for which I'm an administrator but every time I do it fails. Looking at the network tab in the browser, I'm getting a 500 error code with the following payload: {"errorCode":"RemoveMemberFromPrivateChannelFailed"}

The members aren't sole owners of any private channels in the team so I'm not sure what's preventing the operation.