Delay when unlocking encrypted Kubuntu 20.04

[snow]

SCENARIO:
I installed Kubuntu 20.04 with LVM and fully encryted hard disk.
During the boot I enter the hard disk password. The login is then automatically. But the user has an account with a password It works generally. I use also the finger print reader (Thinkpad T495) which works.

PROBLEM:
When I lock the system and then try to unlock by entering the password the following happens:

a) Even if I enter the password and press enter there is a message over the password field to login with the fingerprint reader
b) Then again the password (only ****) shows up again in the password field and looks like it would be wrong or so.
c) Then nothing happens for a while and after about 10 seconds user gets suddenly logged automatically in.

So the login is by far too long and very misleading as the user thinks that something goes wrong and try to enter again the password at step b).

When I use the fingerprint reader everything is OK, you get logged in immediately.

ProblemType: Bug
DistroRelease: Ubuntu 20.04
Package: ubuntu-release-upgrader-core 1:20.04.19
ProcVersionSignature: Ubuntu 5.4.0-40.44-generic 5.4.44
Uname: Linux 5.4.0-40-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.3
Architecture: amd64
CasperMD5CheckResult: skip
CrashDB: ubuntu
CurrentDesktop: KDE
Date: Wed Jul 15 13:56:00 2020
InstallationDate: Installed on 2020-07-14 (0 days ago)
InstallationMedia: Kubuntu 20.04 LTS "Focal Fossa" - Release amd64 (20200423)
PackageArchitecture: all
SourcePackage: ubuntu-release-upgrader
Symptom: release-upgrade
UpgradeStatus: No upgrade log present (probably fresh install)

[snow (mrauschert)]

I created a vdeo demonstrating the problem. In this video I go into standby and then press power button on my computer, enter the password and then the ENTER key only once. Afterwards I do not do anything. Look what happens.

[snow (mrauschert)]

I noticed that before I set up the fingerprint reader the login with password worked very quickely. So the problem seems to be linked to the fp reader setup.

[snow (mrauschert)]

additionally: my current fp reader setup in the /etc/pam.d/common-auth is:

# here are the per-package modules (the "Primary" block)
auth [success=2 default=ignore] pam_fprintd.so max_tries=1 timeout=10 # debug
auth [success=1 default=ignore] pam_unix.so nullok_secure try_first_pass