This could be once again, the “Deming 5%” of true people issues, but it may come back to procedures as well. I’d put some energy into finding out what, in particular, they don’t like about working for that particular team lead. It may come back to lack of input or lack of clarity on what they’re doing. That could mean the team lead needs to use an Action Item List, or clarify the Goal. They could use a Plus/Deltas to brainstorm what’s great about the team and what needs to change. Before you give up, see if the tools can help the team leader.