For at least the last couple of weeks I've had the screen go
completely blank during bootup, after displaying initial messages (I
changed from "quiet" to "debug" for kernel startup). This is with a
luks encrypted root. I saw it under jessie and buster. I blamed
failing hardware (I can't get into the BIOS on boot because the screen
goes black), though I noticed the same behavior in a VM.
I've discovered that if I type my pass-phrase (waiting long enough
that I think things have settled down), the system boots.
So, you might try typing your luks passphrase and see if it helps.
And maybe something has changed in the tools or kernel that's causing
the misbehavior, although jessie hasn't been changing much recently.
Ross