I hate to revive a zombie thread, but I am having the same issue. I am the admin of my org, and we have the E5 plan, but the "checking for insights" never appears. I asked it to track an email last week, and one just now, so I figured at least the one from last week would be available. I've even opened the Viva Insights home page and this seems to be focused on a work/life balance, not tracking emails.
Any help is appreciated