nautilus devices are provided by /usr/lib/gvfs/gvfs-udisks2-volume-monitor, I've already restarted it but one device is still missing. I also tried strace on it, but it only outputs info about mounted devices.
Also, the detection provided by gvfs-mount -l comes from that monitor, but where it gathers information from? If I could determine what is missing/wrong on that detection, may be I could fix it.
I have another very similar device, both are lvm, I checked both with lvdisplay -v -m and there is nothing special about the one that is missing on nautilus.
Despite I can successfully mount it with kvpm, nautilus still ignores it.
Update: The device is missing at tree /dev/disk/ that seems to be populated by udev. So the problem may be fixed by some udev command I think.
Obs.: The missing device had some inode errors but I already fixed them with fsck -vf /dev/dm-6. From this answer, udevadm trigger and vgscan --mknodes also helped on making the device link available again at /dev/<vg>/ (I guess because I had to hard-reset, it went missing there). I fixed it as I believe the monitor may try to read there too. Anyway nothing changed in nautilus even after re-trying actions I detailed previously.