"Timed out waiting for device" & dev-disk-by\x2duuid.swap/service failed with result dependency/timeout?

My server (running Centos Stream release 8) stopped responding to http yesterday evening. I tried to SSH in to it this morning, with no luck, just an empty hung PuTTy screen. I did a automatic reset through my webhost's control panel (Hetzner), and after a few minutes it was back and everything seems to work fine.

I assumed it had ran out of space, and indeed df showed that /dev/md2 was 100% full (even though it says it's 9.8G in size and had 9.5G in it). I deleted some stuff and got that down to 50%. No new files in there though, I feel that's been full for a month or more...

I then had a look in /var/log/messages, to see what was last reported, and found this:

Apr 16 18:47:57 originals systemd[1]: Starting dnf makecache...
Apr 16 18:48:28 originals dnf[87659]: CentOS Stream 8 - AppStream                      20 kB/s | 4.4 kB     00:00
Apr 16 18:48:28 originals dnf[87659]: CentOS Stream 8 - BaseOS                         38 kB/s | 3.9 kB     00:00
Apr 16 18:48:28 originals dnf[87659]: CentOS Stream 8 - Extras                         35 kB/s | 2.9 kB     00:00
Apr 16 18:48:28 originals dnf[87659]: CentOS Stream 8 - Extras common packages         19 kB/s | 3.0 kB     00:00
Apr 16 18:48:29 originals dnf[87659]: Extra Packages for Enterprise Linux 8 - x86_64   33 kB/s |  23 kB     00:00
Apr 16 18:48:30 originals dnf[87659]: Extra Packages for Enterprise Linux 8 - Next -   57 kB/s |  25 kB     00:00
Apr 16 18:48:30 originals dnf[87659]: Google Cloud SDK                                3.8 kB/s | 1.4 kB     00:00
Apr 16 18:48:31 originals dnf[87659]: nginx mainline repo                             160 kB/s | 2.9 kB     00:00
Apr 16 18:48:32 originals dnf[87659]: Metadata cache created.
Apr 16 18:48:32 originals systemd[1]: dnf-makecache.service: Succeeded.
Apr 16 18:48:32 originals systemd[1]: Started dnf makecache.
Apr 16 18:49:28 originals systemd[1]: dev-disk-by\x2duuid.device: Job dev-disk-by\x2duuid.device/start timed out.
Apr 16 18:49:28 originals systemd[1]: Timed out waiting for device dev-disk-by\x2duuid.device.
Apr 16 18:49:28 originals systemd[1]: Dependency failed for /dev/disk/by-uuid.
Apr 16 18:49:28 originals systemd[1]: dev-disk-by\x2duuid.swap: Job dev-disk-by\x2duuid.swap/start failed with result 'dependency'.
Apr 16 18:49:28 originals systemd[1]: dev-disk-by\x2duuid.device: Job dev-disk-by\x2duuid.device/start failed with result 'timeout'.
Apr 16 18:49:28 originals systemd[1]: Timed out waiting for device dev-disk-by\x2duuid.device.
Apr 16 18:49:28 originals systemd[1]: Dependency failed for /dev/disk/by-uuid.
Apr 16 18:49:28 originals systemd[1]: dev-disk-by\x2duuid.swap: Job dev-disk-by\x2duuid.swap/start failed with result 'dependency'.
Apr 16 18:49:28 originals systemd[1]: dev-disk-by\x2duuid.device: Job dev-disk-by\x2duuid.device/start failed with result 'timeout'.

Can anyone suggest what I might need to worry about? Or will it just be down to that /dev/md2 being full, even though that's been full for a while? Or does the above suggest I have an imminent hardware failure?

EDIT:

Looking again at messages I can see that these x2uuid errors occur relatively frequently, both before and since the reboot, and are maybe completely unrelated.

This sounds like your /etc/fstab has an entry that attempts to mount /dev/disk/by-uuid (instead of the expected /dev/disk/by-uuid/SOMETHING). Possibly a stray space between the prefix and the pasted-in UUID, or maybe the UUID is missing from the fstab file entirely.

Run systemctl status 'dev-disk-by\x2duuid.swap' and note the "Loaded:" line. If it says:

Loaded: loaded (/etc/fstab; generated)

then it definitely comes from an /etc/fstab entry. Edit the file and fix the bad entry.