I've noticed in various places in debug logs that the client UUID is being truncated.

[ 5934.778609] Lustre: MGS: Connection restored to aafbfe59-7811-4 (at 10.9.6.193@tcp)

This turns out to be a problem wherever the UUID is shown:

# lctl get_param -n llite.*.uuid
595f3c6a-20ae-4
# lctl get_param -n mdc.*.uuid
595f3c6a-20ae-4

Initially I thought something was wrong with the "safe" string handling in obd_uuid2str(), but it turns out that there is a bug when the client UUID is originally generated in ll_fill_super() because of the use of UUID_SIZE, which is actually the size of the binary uuid_t instead of the ASCII UUID (stored in struct obd_uuid) that is passed between nodes and printed to the logs.