Because of this
Mar 23 17:20:29 DeathStar kernel: BTRFS info (device loop3): read error corrected: ino 0 off 699817984 (dev /dev/loop3 sector 1383216)
Mar 23 17:20:29 DeathStar kernel: BTRFS info (device loop3): read error corrected: ino 0 off 699822080 (dev /dev/loop3 sector 1383224)
Mar 23 17:20:30 DeathStar kernel: BTRFS warning (device loop3): loop3 checksum verify failed on 712540160 wanted 3182DA00 found 19A992C1 level 0
There is a problem with the docker.img file (or its with the cache drive - impossible to tell from the syslog snippet)
But, whether or not the server restarts for you or not, the shutdown was clean based on the snippet, so you can just hit the reset button.
Because of the segfaults, I would run memtest for at least a single pass from the boot menu (ideally more though).
When you actually restart unRaid, post your full diagnostics.