ARP Request Unicasting???

Unicasting ARP Request sounds strange but indeed there are those things.
See Section 2.3.2.1 of RFC1122, "ARP Cache Validation." Specifically,

IMPLEMENTATION:
Four mechanisms have been used, sometimes in
combination, to flush out-of-date cache entries.

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(2) Unicast Poll -- Actively poll the remote host by
periodically sending a point-to-point ARP Request
to it, and delete the entry if no ARP Reply is
received from N successive polls. Again, the
timeout should be on the order of a minute, and
typically N is 2.