can you search for the “Disks” app ? in ubuntu 18.10 it is installed by default and allows you to see more details about your device … where it is / what it is / how it is mounted / how/if it is formated / formating options etc.
maybe try have a look around and see if you can’t install that somehow. it’s a gnome 3.30 app. it also allows to mount/unmount devices. eject power on/off. very good app for novices.
hi there! 
i hope its not too late, but what if ur input language differs now and when it was set up? 
once i made a reinstall cuz of this very reason, then i realized the next time that my keyboard layout differs X’D
This happened to me as well! I use a mechanical keyboard which I hook up to my Librem 13. I turn on number lock to access the numeric keypad. When I remove the Librem 13 from the USB hub where my keyboard is, the number lock is still on, which means that my Librem 13 keyboard enters different characters at the prompt! You can turn off number lock on the Librem 13 with the ‘NumLk’ key on the top right hand side.
I had the same issue where i changed the luks passphrase using pureos disks app and somehow it didnt take properly. Because after boot it still seemed to unlock, but subsequent use of drive caused it to not unlock correctly (for me when the SDCard reader dropped off the bus occasionally).
Using the cryptsetup command and correct password (the one i didnt think it had correctly updated) unlocked my drive.
After that i went into disks and again chnaged the LUKS passphrase. See if it took it this time, otherwise my errors were identical to yours:
Maybe two keyfiles get created and it gets confused which one to take at times.
Intrestingly you cant mount a luks drive using normal mount commands you can only mount the disk using sudo cryptsetup luksOpen /dev/sdb1 cryptdisk command, online most Linux tutorials completely miss that point.
