This doesn’t appear to be the Performance log, but in any case, if this is occurring consistently at midnight, I would suggest it is more than likely related to FillDB’s Historical Counts process. Please see https://bigfix-wiki.hcltechsw.com/wikis/home?lang=en-us#!/wiki/BigFix%20Wiki/page/Troubleshooting%20FillDB%20Operations for more information, but essentially, once a day, FillDB performs some work to count the total number of relevant Fixlets by severity (and total computer count) for use in some specific Web Reports. You can disable this process with the following setting:
HKLM\Software\BigFix\Enterprise Server\FillDB
"UpdateHistoricalCounts" [DWORD]=0