(In reply to Alexander Nolting from comment #26)
> Hello Thomas,
> 
> I went through the new debug log and figured out the
> systemd-ask-password-plymouth in line 945 - 15:52:20 is called and startup
> is finished in line 2952 - 15:52:24 but I don't see any passphrase prompt.
> 
> If I'm checking systemd for active units then I find the unit is active and
> still waiting.
> 
> Also weird is, that before the issue occurred changing between console and
> plymouth while booting showed my everytime the passphrase dialog - on
> console and plymouth - which ever is active at this moment.
> 

The device timeout is still visible:

-->--
Oct 07 15:54:08 linux-gwd0 systemd[1]:
dev-disk-by\x2did-ata\x2dSamsung_SSD_840_Series_S14GNEAD229172E\x2dpart3.device:
Job dev-disk-by\x2did-ata\x2dSamsung_SSD_840_Series_S14GNEAD229172E\x2
dpart3.device/start timed out.
Oct 07 15:54:08 linux-gwd0 systemd[1]: Timed out waiting for device
dev-disk-by\x2did-ata\x2dSamsung_SSD_840_Series_S14GNEAD229172E\x2dpart3.device.
-- Subject: Unit
dev-disk-by\x2did-ata\x2dSamsung_SSD_840_Series_S14GNEAD229172E\x2dpart3.device
has failed
-- Defined-By: systemd
-- Support: http://lists.freedesktop.org/mailman/listinfo/systemd-devel
-- 
-- Unit
dev-disk-by\x2did-ata\x2dSamsung_SSD_840_Series_S14GNEAD229172E\x2dpart3.device
has failed.
-- 
-- The result is timeout.
Oct 07 15:54:08 linux-gwd0 systemd[1]: Dependency failed for Cryptography Setup
for cr_home.
--<---

It is quite odd that your system with a fast ssd disk takes more than 2 minutes
to boot. Not sure what is causing this delay.
You might want to check via:

systemd-analyze blame

wheter some systemd services are stalling.
However, in order to solve the device timeout, can you please set:

x-systemd.device-timeout=300

in the fourth field of /etc/crypttab?