We're moving from level 5 to 6 in our campaign, but I've noticed that the campaign overview still lists them as level 5 and when I go to the encounter builder, it ALSO still lists them as 5. Does it take a while to update? Is there something I / they need to do? I don't think we've had this issue before.

Any encounters you've previously built have to be manually updated as characters level up. The campaign view, as far as I know, reflects the current state of the characters. Have the players locked in their new level yet? 

Ok thanks for the note about the encounters. I'm not sure how the players lock in their new level. But after reading your comment I did go back and check one more time on the campaign view and it now correctly reflects their levels. Maybe it takes an overnight to have it show up / update and I had just never noticed before?

Locked in meaning they've adjusted their character level. I really can't speak to how long it takes to reflect changes in the campaign view as I've never checked immediately.