I'm on FDE, but I don't think I'm using UEFI. My kernel is linux-current, but the segfault also occured on -lts yesterday.

the output with CBM_DEBUG=1:

root@solus # CBM_DEBUG=1 clr-boot-manager update
[INFO] cbm (src/bootman/bootman.c:L437): Current running kernel: 4.13.7-27.current
Segmentation fault (core dumped)

root@solus # journalctl -r --since "10 seconds ago"
-- Logs begin at Mon 2017-09-04 20:50:15 BST, end at Sat 2017-10-14 22:00:07 BST. --
Oct 14 22:00:07 solus-feb2017 kernel: audit: type=1701 audit(1508014807.402:87): auid=1000 uid=0 gid=0 ses=2 pid=9967 comm="clr-boot-manage" exe="/usr/bin/clr-boot-manager" sig=11 res=1
Oct 14 22:00:07 solus-feb2017 kernel: clr-boot-manage[9967]: segfault at 10 ip 00007f6b62a681b1 sp 00007ffe318d07e0 error 4 in libblkid.so.1.1.0[7f6b62a50000+44000]
Oct 14 22:00:07 solus-feb2017 audit[9967]: ANOM_ABEND auid=1000 uid=0 gid=0 ses=2 pid=9967 comm="clr-boot-manage" exe="/usr/bin/clr-boot-manager" sig=11 res=1

I tried it about five times before touching util-linux, including once on the linux-lts kernel, with a segfault every time. I only looked at the journalctl for two of them, but both were libblkid.so related errors.

A sneaky workaround which I wouldn't rely on forever, but it works for now:

This is an upstream/amdgpu issue apparently. From Phoronix:

Somewhat hopeful update: I was able to get a tty by adding the nomodeset flag during boot, then pressing ctrl-alt-f1 after the password was entered. Looking through the journalctl log, amdgpu didn't load (but I didn't expect it to with nomodeset) and lightdm complains it can't find /var/lib/lightdm-data then fails.
It seems lightdm can start without that directory, since it does not exist on kernel 4.12.14 either, so perhaps lightdm's failure is due to nomodeset, or maybe something else.
I'm still not sure whats happened, but I'm inclined to say it's X.org related

This resurfaced again today; unplugging the secondary monitor to reset the driver made it stop again. An eopkg update had happened yesterday, and this was my first reboot since.

This issue has apparently stopped after adding the following kernel flags

λ ~/  cat /etc/kernel/cmdline
amdgpu.powerplay=1
amdgpu.dpm=1

which enable amd's powerplay and 'dynamic power management' respectively (their default value is -1 -- autodetect)
I added these after doing the unplug/plug in of my monitor as described in the first post, so it could have just been that too.

In T524#59733, @STiAT wrote:

Maybe due to the reason that I've windows on a seperate disk (not the same solus is installed on), but it does not work as I'd expect it.

am having the same issue with this same configuration