Finally, you might take a look at the actual team dynamics. Do people like each other? Are they friendly? Do they collaborate on projects, or is every person working on something independently? Is there banter in the chat room, in emails? Do they have a good working relationship with other adjacent departments, and with their product managers? These are little things, but even very professional groups tend to have a degree of personal connection between the members. A bunch of people who never talk to each other and are always working on independent projects are not really working as a team. There would be nothing wrong with that if the team were performing well, but given that they’re not, this may be contributing to your problem.