The peak limit is a value derived from the logs/day licensing. Although exceeding peak limit is permitted, if this peak limit is consistently exceeded, it is an early warning that you are at risk of exceeding the daily licensed limit.
To see the derived limits:
FortiAnalyzer # get sys loglimits
GB/day : 1
Peak Log Rate : 50 #<--- derived value
Sustained Log Rate : 30 #<--- derived value
Fortinet Technical Support