S.M.A.R.T. Status: Not supported.
The USB bridge chip set you're using doesn't pass through ATA commands. Therefore you can't poll the built-in SMART feature in the hard drives that periodically do testing and might give an idea if this is a disk problem at a physical level - like sector problems or read problems.
They both draw power from USB. I have attached another screenshot!
Each drive connects to just one USB port? This is widely regarded to be unreliable. I know it seems like it's just encryption related, but so often drives draw more than a single USB bus can power. Often such USB only cases will come with cable that lets you plug into two separate USB ports so the drive gets enough power from two buses instead of one.
So my first suspect is the drive isn't getting enough power, and occasionally gets wonky. And then the kernel is getting P.O.'d. although I'm not sure why - not a particularly elegant way to get annoyed.
Have you tried disconnecting the drives instead of forcing a shutdown of the computer to see if the system recovers?
Basically, all of these forced shutdowns are likely causing corruption of the journal and or the directory on the disks. And adding encryption, corrupted encrypted extents on disk may cause the problem you're experiencing as well.
If these enclosures came with external power adapters, or a way to connect to two *powered* USB ports, I would try that. And only use one at a time if you're using USB power only.
Quite honestly, this is one of the reasons why I'm not a fan of USB enclosures. Most of the bridge chip sets suck, and make it impossible to do SMART tests on the disks inside of them. And then there's the question of power consumption and if the disk is getting what it needs.
So to distill this down into two suggested paths:
1. If you can use an external power adapter for the enclosures, or two USB ports for each enclosure, do that. Best practices says that at a minimum the disk needs to be unlocked, mounted, and then repaired with Disk Utility. Ideally you'd unlock it, move data off, repartition the disk and reformat (setting it to the encrypted variety of HFS+) and then move data back. That's the only way to be sure you're gotten rid of corruption either at an encryption level or file system level.
2. Find different enclosures for the drives that have external power. You'll still need to do file system repair at least, ideally move data off the drive, repartition with 1 encrypted HFS+ partition, then move the data back.