found performance statistics disapplear on bigip 6400

I check performance graphic on my bigip 6400, found there are no data on graphic. version is 9.3.1 I know there is a bug of 32 bit system ,after 497 days problem. but this 6400 has running for more than two years, I just find this problem. it i hit this bug,I thought after 497 days i should immediatly found this problem, but i didn't, I found this problem afer two years,why after almost 730 days , I just find this prolem ,not just after 497 days.