did you consult the FOS Message Reference Guide?
Do you see this behavior in the same port in all the switchs? Have to tried to move the device connected to that port to a different port to see if the events persist? What's connected at the other end of the link to that port?
I found DEFECT000281102 that reports the behavior you've described but as per the defect notes, it was detected in FOS 6.4.0 and a fix was applied in 6.3.2a, but did not find anything related to a fix for 6.4 code family.
as mentioned by ralf, i would work first with Message Reference Guide in order to identified the issue.
check first at all with command "switchstatuspolicyshow" if some components Marginal or Down are in range.