Thanks for a detailed and very helpful report.
FreedomBox tried obtain information from udisks2 to show a warning about remaining disk space in case it is low. The information return from udisks didn’t contain a partition with ‘/’ as the mount point. I don’t know a situation in which this can happen. This is probably and error that is the result of log number 2 above (the two event seem to have occurred more than 1 hour part though). Could you provide the output of udisksctl dump? (Please remove any UUIDs from the output as the could prove privacy sensitive).
The second error should not have occurred at all. The directory does not typically exist until any of udisks2 modules are installed (provided by udisks2-* packages). Checked on two different machines.
user@freedombox:~$ ls /usr/lib/arm-linux-gnueabihf/udisks2
ls: cannot access '/usr/lib/arm-linux-gnueabihf/udisks2': No such file or directory
root@mybox:/usr/lib# ls /usr/lib/x86_64-linux-gnu/udisks2
ls: cannot access '/usr/lib/x86_64-linux-gnu/udisks2': No such file or directory
After installing udisks2-btrfs:
root@mybox:/usr/lib# ls /usr/lib/x86_64-linux-gnu/udisks2/modules/libudisks2_btrfs.so
/usr/lib/x86_64-linux-gnu/udisks2/modules/libudisks2_btrfs.so