This happens from time to time. Its most likely they have their radar set to “clear air” mode.
Either that or they could be having a technical issue, thermal inversion, etc...
As we cannot look at that individual radar on that site, its going to be hard to tell exactly, but I don't think its any big “event”.
I cant remember but I think its some type of Doppler radar effect I was told , there were a bunch up around Wilmington N.C. offshore recently, that's
the story I was given when I asked, I really don't know.