[atlas] Link-Local ICMP messages for Atlas probe

I've been hosting an Atlas probe since February 2019. I have native
dual-stack gigabit fibre internet service and my router is pfSense.
Recently, I noticed that there are hundreds of messages in the log of the
router like the following:

Aug 12 22:38:54 kernel cannot forward src fe80:5::1cce:5fff:fe02:61b6, dst
2001:569:585f:b00:1:b3ff:fedd:9f24, nxt 58, rcvif hn0, outif hn1
Aug 12 22:36:06 kernel cannot forward src fe80:5::e65d:370f:fc45:b5ba, dst
2001:569:585f:b00:1:b3ff:fedd:9f24, nxt 58, rcvif hn0, outif hn1
Aug 12 22:11:31 kernel cannot forward src fe80:5::3c01:20ff:fee5:f601, dst
2001:569:585f:b00:1:b3ff:fedd:9f24, nxt 58, rcvif hn0, outif hn1
Aug 12 17:45:08 kernel cannot forward src fe80:5::2a0:a50f:fcdb:db7c, dst
2001:569:585f:b00:1:b3ff:fedd:9f24, nxt 58, rcvif hn0, outif hn1
Aug 12 15:47:09 kernel cannot forward src fe80:5::2a0:a50f:fcb9:c28e, dst
2001:569:585f:b00:1:b3ff:fedd:9f24, nxt 58, rcvif hn0, outif hn1
Aug 12 08:13:04 kernel cannot forward src fe80:5::2a0:a50f:fc8a:8134, dst
2001:569:585f:b00:1:b3ff:fedd:9f24, nxt 58, rcvif hn0, outif hn1
Aug 12 06:55:33 kernel cannot forward src fe80:5::bac2:530f:fc39:164a, dst
2001:569:585f:b00:1:b3ff:fedd:9f24, nxt 58, rcvif hn0, outif hn1
Aug 12 03:39:05 kernel cannot forward src fe80:5::2a0:a50f:fc8a:85c0, dst
2001:569:585f:b00:1:b3ff:fedd:9f24, nxt 58, rcvif hn0, outif hn1
Aug 12 01:17:54 kernel cannot forward src fe80:5::e6fc:820f:fcea:2016, dst
2001:569:585f:b00:1:b3ff:fedd:9f24, nxt 58, rcvif hn0, outif hn1
Aug 12 00:55:09 kernel cannot forward src fe80:5::ee9e:cd0f:fc0d:79d4, dst
2001:569:585f:b00:1:b3ff:fedd:9f24, nxt 58, rcvif hn0, outif hn1
Aug 11 15:47:11 kernel cannot forward src fe80:5::4271:830f:fce5:7fa, dst
2001:569:585f:b00:1:b3ff:fedd:9f24, nxt 58, rcvif hn0, outif hn1
Aug 11 15:25:42 kernel cannot forward src fe80:5::bac2:530f:fcd4:fdd2, dst
2001:569:585f:b00:1:b3ff:fedd:9f24, nxt 58, rcvif hn0, outif hn1
Aug 11 07:33:53 kernel cannot forward src fe80:5::cd08:c204:cc63:2d32, dst
2001:569:585f:b00:1:b3ff:fedd:9f24, nxt 58, rcvif hn0, outif hn1
Aug 11 06:17:19 kernel cannot forward src fe80:5::fe33:420f:fcdc:5932, dst
2001:569:585f:b00:1:b3ff:fedd:9f24, nxt 58, rcvif hn0, outif hn1
Aug 11 04:49:00 kernel cannot forward src fe80:5::7e25:860f:fc44:6742, dst
2001:569:585f:b00:1:b3ff:fedd:9f24, nxt 58, rcvif hn0, outif hn1
Aug 10 22:41:25 kernel cannot forward src fe80:5::9ca0:15ff:fe87:842e, dst
2001:569:585f:b00:1:b3ff:fedd:9f24, nxt 58, rcvif hn0, outif hn1
Aug 10 14:38:59 kernel cannot forward src fe80:5::c80a:daff:fe92:b8b7, dst
2001:569:585f:b00:1:b3ff:fedd:9f24, nxt 58, rcvif hn0, outif hn1
Aug 10 10:55:07 kernel cannot forward src fe80:5::2a0:a50f:fc8a:6ea0, dst
2001:569:585f:b00:1:b3ff:fedd:9f24, nxt 58, rcvif hn0, outif hn1
Aug 10 08:57:19 kernel cannot forward src fe80:5::46aa:500f:fceb:ad66, dst
2001:569:585f:b00:1:b3ff:fedd:9f24, nxt 58, rcvif hn0, outif hn1
Aug 10 05:47:09 kernel cannot forward src fe80:5::b68a:5f0f:fcb2:1040, dst
2001:569:585f:b00:1:b3ff:fedd:9f24, nxt 58, rcvif hn0, outif hn1
Aug 10 03:24:58 kernel cannot forward src fe80:5::2a0:a50f:fcb6:5ea2, dst
2001:569:585f:b00:1:b3ff:fedd:9f24, nxt 58, rcvif hn0, outif hn1
Aug 10 03:08:55 kernel cannot forward src fe80:5::2a0:a50f:fc90:9d4, dst
2001:569:585f:b00:1:b3ff:fedd:9f24, nxt 58, rcvif hn0, outif hn1
Aug 10 00:17:07 kernel cannot forward src fe80:5::e65d:370f:fc44:15ba, dst
2001:569:585f:b00:1:b3ff:fedd:9f24, nxt 58, rcvif hn0, outif hn1
Aug 10 00:07:07 kernel cannot forward src fe80:5::2a0:a50f:fcb7:7c, dst
2001:569:585f:b00:1:b3ff:fedd:9f24, nxt 58, rcvif hn0, outif hn1

The messages occur in groups of three, spaced a few seconds apart.

All of the messages start with fe80:5. Even if I strip off the "5", none of
them seem to convert into MAC addresses, so I can't use that to figure out
what type of device is pinging the probe.

There are no entries in the NDP table corresponding to these messages.

I have no idea how long this has been happening. I only noticed it when I
was setting up a new server to host pfsense.

My probe is RIPE-Atlas-Probe-52209.

I'm interested to know if anyone else has experienced this.
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