Aha, I think I figured it out...
I noticed that the two new LUNs were the first two LUNs created on the second node of our storage cluster, and that they were appearing as multiple paths for the first two LUNs created on the first node of the storage cluster, in the same order. That is, the first LUN of node 1 and the first LUN of node 2 were showing up as the same LUN, and the same goes for the second LUN of both nodes.
I discovered that the Identifier field in ESXi corresponds to the SCSI_id of the LUN, and by default, the Linux tgtd daemon assigns the SCSI ids starting with 00010001 and counting up, 00020001, 00030001, etc. So the first two LUNs on both nodes have the same SCSI id, 00010001 and 00020002. I believe that I can manually specify the SCSI ids to override this default behavior, and that will address this issue.
I'll try that change soon and post back with my results. Thanks.
Regards,
Jon Heese