First of all: Congratulations and all the best, Robby!
Not sure, if the following is related to the topic discussed here, but possibly it is.
I am on Slackware64 13.1 stable. When I boot my machine, while an external USB disk with a LUKS encrypted partition on it, a dialog asking for the LUKS passphrase pops up in KDE. I enter the passphrase, and the dialog is closed. Nothing else seems to happen, and there's no Dolphin window showing the file system.
Now, on the left side in Dolphin there's an icon for the LUKS device. Clicking with the left mouse button on it has no effect. But if I click onto it with the right mouse button, I can select an option to disconnect the device. Doing so and then clicking on the icon with the left mouse button brings up the passphrase dialog, again. This time the passphrase is accepted and a Dolphin window opens showing the file system on the encrypted partition on the USB device. Sometimes this fails, but in most cases it works, while the first attempt right after starting KDE almost always fails.
However, this seems all have to do with a timing problem. If I wait a couple of minutes after starting KDE, before I enter the LUKS passphrase in the dialog window, it usually works as expected. It fails, if I do it immediately when the passphrase dialogs pops up.
Plus: I don't have the problem, if I boot with no USB disk connected. If I connect the device after starting KDE, everything is working just fine in nine out of ten cases (not in ten out of ten, I have to say).