since quite a while initrd for newer kernel do not boot/mount my encrypted
rootfs anymore.

I'm still running kernel 5.3.12-2-default.
first time I tried to boot new kernel and failed was with
kernel-default-5.5.7-1.1,
then later with kernel-default-5.7.1-1.2 and now with kernel-default-5.8.0-1.1

these are the messages from journalctl for the failed boot of 5.8.0:

Aug 28 21:13:23 hl systemd[1]: Found device Samsung_SSD_850_EVO_2TB 5.
Aug 28 21:13:23 hl systemd[1]: Found device Samsung_SSD_850_EVO_2TB 3.
Aug 28 21:13:23 hl systemd[1]: Reloading.
Aug 28 21:13:23 hl systemd[1]: Starting Cryptography Setup for cr_sda5...
Aug 28 21:13:23 hl systemd[1]: Started Forward Password Requests to Plymouth.
Aug 28 21:13:32 hl systemd-cryptsetup[433]: Set cipher aes, mode
cbc-essiv:sha256, key size 256 bits for device /dev/sda5.
Aug 28 21:13:32 hl systemd-cryptsetup[433]: device-mapper: reload ioctl on  
failed: No such file or directory
Aug 28 21:13:32 hl systemd-cryptsetup[433]: Failed to activate with specified
passphrase: Invalid argument
Aug 28 21:13:32 hl systemd[1]: systemd-cryptsetup@cr_sda5.service: Main process
exited, code=exited, status=1/FAILURE
Aug 28 21:13:32 hl systemd[1]: systemd-cryptsetup@cr_sda5.service: Failed with
result 'exit-code'.
Aug 28 21:13:32 hl systemd[1]: Failed to start Cryptography Setup for cr_sda5.
Aug 28 21:13:32 hl systemd[1]: Dependency failed for Local Encrypted Volumes.
Aug 28 21:13:32 hl systemd[1]: cryptsetup.target: Job cryptsetup.target/start
failed with result 'dependency'.

and here the msgs for successfully booting into 5.3.12-2 again:

Aug 28 23:29:19 hl systemd[1]: Found device Samsung_SSD_850_EVO_2TB 5.
Aug 28 23:29:19 hl systemd[1]: Found device Samsung_SSD_850_EVO_2TB 3.
Aug 28 23:29:19 hl systemd[1]: Starting Cryptography Setup for cr_sda5...
Aug 28 23:29:19 hl systemd[1]: Reloading.
Aug 28 23:29:19 hl systemd[1]: Started Forward Password Requests to Plymouth.
Aug 28 23:29:25 hl systemd-cryptsetup[476]: Set cipher aes, mode
cbc-essiv:sha256, key size 256 bits for device /dev/sda5.
Aug 28 23:29:26 hl systemd[1]: Finished Cryptography Setup for cr_sda5.
Aug 28 23:29:26 hl systemd[1]: Reached target Local Encrypted Volumes.


both initrd are freshly created with up-to-date dracut:
-rw------- 1 root root 18584060 Aug 28 23:10 /boot/initrd-5.8.0-1-default
-rw------- 1 root root 17643032 Aug 28 23:11 /boot/initrd-5.3.12-2-default


what is "missing" in this msg in between "on" and "failed:" (between the two
extra spaces)?

Aug 28 21:13:32 hl systemd-cryptsetup[433]: device-mapper: reload ioctl on  
failed: No such file or directory
                                                                          ^^^