I only have about 10 DHCP leases. When I go to Status -> DHCP Lease, I see that my IP camera sometimes the "online" status is OFFLINE, but "lease type" is ACTIVE. But I am pretty sure my camera is online, coz I can use my browser to connect to the camera just fine. I am not sure how pfsense determine if it's offline, and if it only refresh the DHCP lease list every few minutes. Also, if this is the reason that pfsense thinks my ip camera is offline and release the IP lease.
I turned off the logging from writing to disk, because I had memory issue. I just turned it back on, will monitor why my IP changes.