I have these messages as well but have been able to figure out what causes them. Unfortunately your explanation does not apply to my setup since I do not have any Apple devices on my network.

I get messages like these:
arp: 10.0.0.23 moved from 02:ff:20:00:0a:0a to 1c:98:ec:0e:c7:70 on epair5b
arp: 10.0.0.23 moved from 02:ff:20:00:09:0a to 1c:98:ec:0e:c7:70 on epair4b
arp: 10.0.0.23 moved from 1c:98:ec:0e:c7:70 to 02:ff:20:00:0a:0a on epair5b
arp: 10.0.0.23 moved from 02:ff:20:00:0a:0a to 1c:98:ec:0e:c7:70 on epair5b
arp: 10.0.0.23 moved from 1c:98:ec:0e:c7:70 to 02:ff:20:00:08:0a on epair3b
arp: 10.0.0.23 moved from 02:ff:20:00:0a:0a to 1c:98:ec:0e:c7:70 on epair5b
arp: 10.0.0.23 moved from 1c:98:ec:0e:c7:70 to 02:ff:20:00:0a:0a on epair5b
arp: 10.0.0.23 moved from 02:ff:20:00:0a:0a to 1c:98:ec:0e:c7:70 on epair5b

10.0.0.23 is the main IP of my FreeNAS server and 1c:98:ec:0e:c7:70 is the MAC of the hardware NIC. All devices on my network have static DHCP leases (including 10.0.0.23) and I have never had any problems accessing either the server or any of the jails. Not sure if this is a problem but it bugs me that I receive these log messages every day, and it is not related to rebooting the server or jails since I do not do that very often.