For the RF Health report, problem radios are radios that violate 2 or more thresholds.
The following theshold values are hardcoded for the RF Health Report:
average noise greater or equal to -80
average channel utilization greater or equal to 75
MAC / Phy errors greater or equal to 1000
Interfering device count greater or equal to 1
Most often, you'll see that the MAC/Phy errors and Interfering device counts are the triggering thresholds since they are the easiest to set off in most environments.