More often then I would like, one or more of our build agents dies/croaks/barfs/quits for unknown or unexpected reasons. When this occurs, our CI builds will remain green (or red) and display a spinning build icon, as opposed to a check mark. After a bit of time (usually way longer than I'd like) someone notices that the builds have not recently completed, or done anything for that matter. Only after you click on a build are you then notified that:

No agents can run this build.

But what? I was just looking at a spinning icon, is Bamboo confused, or just trying to confuse users?

I would suggest that if a build is in a state of "No agents can run this build" it gets a new icon, other than a spinning arrow, perhaps one which conveys some sense of urgency and concern. Like a yellow triangle or similar.