Throughput graph showing frame utilization but not throughput

I'm finding that some of the APs I have cnMaestro keeping an eye on aren't listing throughput in the throughput graph.  They are showing the frame utilization, so I know connectivity to the APs is good.  They're even giving real time throughput values on the monitoring screen, but the graph just shows the lines of frame utilization with not shadows for throughput.

It seems to mostly be a problem with 900 450i APs, but I have one 900 which is showing throughput in the graph and one 36 PMP450 AP which isn't, so it's not 100%.

All the APs are running 15.0.2, and I'm using cnMaesto On Premises 1.4.0-r11.