Can you pl check this suggestion:
The IS system task “Statistics Log” should execute service “pub.event.stats:logToFile” in regular intervals (default 60 secs). Review system task status in IS Admin > Server > Scheduler > View System Tasks.
The task has low priority in IS and when IS resources become very limited, IS internally kicks out the “Statistics Log” system task. This is by design and no problem or bug. So verify if something that was very IS resource intense (in terms of thread allocation, CPU usage, JVM full garbage collection etc.) was going on at the time where stats data is missing.
Also check the current subscription status of “Statistics Log” system task by running service pub.event:getSubscribers and enter input “Stat Event”. If the subscription is disabled the stats.log file is not populated any more.
You can later re-enable the subscription in Designer > Service Development perspective. Click on a Server Node --> Properties and change “Enabled” setting to “true” for event type “Stat Event”.
Based on the above if still an issue raise a ticket with SAG as part of 9.5 setup issues.