I will paraphrase a translation of the Jet World Masters (JWM) report from the PowerBox (PB) team member:
Reports of radio interference started on day one or two of the event. PB team was not aware of any interference as they were too busy fueling, charging and flying.
The clamor increased when Vitaly Robertus had trouble landing his practice jet due to interference, which ended up damaging the model.
Competitors were told to monitor Fail Safe and Lost Frames. PB team member says at home he typically sees 1 to 150 Lost Frames, at the JWM his lost frames were between 750 and 1400.
Under pressure from the competitors, the event organizer summoned (very quickly) a vehicle with a spectrum analyzer. As a result of the analysis, the event security monitoring cameras were shut down. Afterwards, Lost Frames went down to 80 up to a maximum of 600 each flight. Despite the improvement, multiple competitors with various radio systems experienced interference. Maneuvers were allowed to be re-flown in these cases.
There was no correlation between the interference and distance. It happened mostly at a range between 100m and 300m.
PB team logged 40 flights during the event without any radio issues, no Fail Safes. They are obviously very happy about this and consider the experience good first-hand evidence of the Core radio's resiliency in a challenging RF environment.
My comment: The original post did not point fingers, or disparage by name, any of the other radio systems at the event.
I'm just the translator...