Make sure to disconnect all other external drives. It may be possible to mount the volume as Read-Only using the command line. It sounds like the file system got corrupted from the unexpected disconnect. I did not understand the procedure sorry, when I go to disk utility I can see the drive but it's not mounted it's light gray and In the owners tab it says disabled, Make sure to have frequent and regular backups of both your boot drive and all external media that contain important & unique data. I know in theory APFS should be a much better & more reliable file system, but unfortunately it is still quite new with some quirks that still need to be resolved both with APFS and First Aid. I highly recommend using HFS+ unless there is a specific reason you need to use APFS. I do not have any faith in the reliability of the APFS file system since I've encountered so many issues with it on our organization's Macs which required completely erasing the drive since First Aid was unable to fix the file system issues. If the volume is unlocked, then you can try to manually mount the volume by forcing 'ReadOnly'. I'm not at a Mac right now so this is just some general suggestions I'm using from memory which may not be 100% accurate, but it should point you in the right direction.

Where you replace 'diskNsY' with the actual drive ID ('N') and volume ID number ('Y'). Maybe even this will work as well: diskutil info diskN Where you substitute 'diskN' with the actual drive identifier which I believe will list the status of the encrypted volume. If the drive shows up when you run diskutil list external

Macbook encryption problems