Mint 19 Encrypted Volume Passphrase Issue

[nonrepeatedmeme]

I've been searching around and haven't found exactly my issue, so I thought I would ask.

I just installed Mint 19 (Cinnamon, x86_64) on my workstation. My /home is on an encrypted volume that has been around for quite some number of years and has worked well through various versions of Ubuntu. The passphrase for /home has previously always been prompted for upon boot by the boot screen GUI and the volume is mounted when the correct passphrase is given. Oddly, with Mint 19 the GUI prompt for the passphrase appears and seems to take my passphrase, but then the volume doesn't mount and I'm dropped to a recovery shell. Running cryptdisks_start yields a shell prompt for my passphrase. After entering the passphrase the volume is mounted correctly and <ctrl>-d out of the shell continues with Mint 19's start-up.

My passphrase is quite long. I'm wondering if the GUI prompt for the passphrase has some sort of hard-coded length limitation? I didn't see any documentation that mentions anything like this and it does seem odd that a later distro would have restricted the passphrase length, but it really does seem like the GUI isn't accepting what I type. Interestingly, I don't see any failures in any of the logs...but then to be fair I also don't see anything that looks like a success either, so maybe this sort of thing is simply not logged?

Any clues on where I should be looking to debug this issue are greatly appreciated.