CoreStorage logic volume failed to mount

I have an encrypted hfs+ external SSD. When I plug it into my mac and, it prompts for my password, but after I enter it nothing happens.

I tried this in terminal:

I ran into this. In my case it seems the problem was the mac wanted to run a filesystem check on it. After finding the fsck process and killing it, I could then mount the drive properly.

$ ps -ef | grep fsck  
$ kill [pid from above] 

1. Maybe check to see if you have any softwares running that block mounts, such as "disk arbitrator". In my case I forget to disable it, and after quitting it my disk mounted. (However, it may not show up in Finder, depending on how the system want it to work. Go to /Volumes/ to check whether the disk is mounted.)
2. Next, restart in another system (recovery HD may be a good option) and check whether the disk will mount or not. If it mount, than it's your system's fault.
3. After restarting to your default system, see if it will mount. If not, try if resetting SMC, resetting NVRAM/PRAM, and booting up in safe mode works.
4. If not, maybe reinstall the system.
5. If all above don't work, contact Apple Support, or ask a macOS expert.

Note: What I've provided is a standard procedure to solve most minor problems. It may not work and you should backup before doing any potentially dangerous tasks.