I just checked three of my UID customers (all set up the same way with a single transit VLAN).
2 of them were correct. 1 showed the same anomaly with client count as you showed.
I'm going to have a think about what could be the possible difference between the working and non-working. They are all running similar firmware versions.
The working ones were using MX250s and MS250s for their L3 routing. The one that didn't work was using MX100 and MS350-24Xs.