In short
Almost always this is either ground clutter near the radar station itself, or rain that's falling from a higher altitude and evaporating before it reaches the ground. It isn't a fault with the page.
Radar doesn't measure rain on the ground. It measures moisture reflecting off a beam that travels in a straight line while the earth curves gently away beneath it, so the further you are from the station, the higher above the ground that beam is actually sampling.
Two common causes
Close to a radar station, solid objects such as hills, buildings, wind turbines, or even birds and insects can scatter the beam back and show up as a patch of light green that never quite matches real weather. Further out, the beam can be sampling rain that's still high in the cloud and evaporates before it hits the ground, a phenomenon meteorologists call virga.
How to tell the difference
Real rain moves. Play a few frames on the timeline and a genuine system tracks steadily in the direction of the wind, building or fading gradually. Clutter tends to sit in exactly the same spot, frame after frame, usually right around the radar site marked on the map, regardless of what the wind is doing.
Related reading
See How do I use the Rain Radar? for the full picture, including the timeline and range controls.