It is very rare, but being one of Jim's FR FB admins, I've had 2 FR 'Zotees' plead their case to me on FB that they were mistakenly zotted (long time FReepers in good standing), I brought it to JR's attention here and they were reinstated.
So I suspect it happens 0.000000001% of the time. 😃
Were they zotted because of a hot debate with other posters?