Everything looks fine to me, your firewall is not paging or swapping due to a shortage of free memory as shown by top.
Looks like normal utilization of excess memory for buffering/caching that grows over time, but that memory can be freed instantly if it is needed for code execution which happened a few times and caused the sudden drop in memory utilization in your graph. After a reboot memory utilization will look much lower and slowly grow as it is utilized for buffering/caching; this is expected and welcome behavior as long as your firewall is not dipping into swap space.
As Phoneboy said we need to see Super Seven outputs, especially free -m.
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