Although these look like basic things, things like these tend to fail a lot even on big companies!
They are inside a box.
To keep people around, leave the box, lower the priority on work, at least for a few moments and focus on people. Look around, look at people’s faces and check if they are happy or if they’re struggling. Unless everyone’s playing poker, just by looking at people you can see how they are doing. Talk to them, ask how things are working out for them. And sometimes invite people for tacos or pizza, have fun moments and relax.