From the logs, I see the following:
1) REED attempts to become a ROUTER by sending an Address Solicit message.
[0000468531] [MLE] [INFO]-MLE-----: Sent address solicit to b800
2) REED successfully sent the message to ROUTER (RLOC = 0xf800).
[0000468546] [MAC] [INFO]-MAC-----: Sent IPv6 UDP msg, len:73, chksum:c39f, to:0xf800, sec:yes, prio:low, rss:
[0000468559] [MAC] [INFO]-MAC-----: src: fdde:ad00:beef:0:0:ff:fe00:f801
[0000468568] [MAC] [INFO]-MAC-----: dst: fdde:ad00:beef:0:0:ff:fe00:b800
3) LEADER overhears the Address Solicit message being sent from REED to ROUTER.
[0000468543] [MAC] [INFO]-MAC-----: Frame rx failed, error:UnknownNeighbor, len:58, seqnum:12, type:Data, src:0xf801, dst:0xf800, sec:yes, ackreq:yes
4) REED overhears ROUTER forwarding the Address Solicit message to LEADER (RLOC = 0xb800).
[0000468577] [MAC] [INFO]-MAC-----: Frame rx failed, error:DestinationAddressFiltered, len:58, seqnum:70, type:Data, src:0xf800, dst:0xb800, sec:yes, ackreq:yes
5) LEADER overhears the Address Solicit retransmission being sent from REED to ROUTER.
[0000512695] [MAC] [INFO]-MAC-----: Frame rx failed, error:UnknownNeighbor, len:58, seqnum:16, type:Data, src:0xf801, dst:0xf800, sec:yes, ackreq:yes
The Wireshark packet trace also confirms that the Address Solicit message is getting sent to the LEADER and an IEEE 802.15.4 ACK is sent in response.
It appears the Address Solicit message (i.e. step 4) is not being received by LEADER, but it is not clear why. Can you debug your radio layer to see if the packet is being properly received and passed up to OpenThread?
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Jonathan Hui