Recovery Mode: FireVault psswd unrecognised and CoreStorage not found
If you have access to another mac, a potential way to be able to back up your data is to boot in target disk mode https://support.apple.com/en-us/HT201462. This will mount your internal HD on the host mac like it would a normal external HD and the OS will immediately prompt you to unlock it using your FileVault pw. I have encountered basically this same bug you are describing in the past and have had success unlocking with this method, even if it fails from recovery. 

If you don't have another Mac handy, you can also reset your FileVault pw (I understand that you know it, but this method may still get you back into the machine) by opening terminal from the utilities menu in recovery (or internet recovery, whichever) typing resetpassword, hitting enter and following the prompts. However, if you don't have your recovery key or apple ID access set up this method won't be much help. Good luck!