Boot freeze after update but can boot system from Tumbleweed install USB key

Hello,
I made an update of my laptop last week (as for my desktop one) using zypper dup.
Since, I can’t “boot”. Grub appears, I can select the kernel, and then, nothing. The only console message I see is when I plug an USB device, or press Ctrl-Alt-Suppr (if not, screen completely black).

Hint : I can boot/normally use the laptop system from Tumbleweed install disk.

fstab and crypttab (/home) are correct (I use partition ID, EFI, only one disk, a SSD), grub configuration seems ok.
I reinstall everything (twice yesterday), no change.

For such stuck startup, I do not have any /var/log files to read to do the troubleshooting, so I think the system seems to not be able to open the filesystem (all in ext4).

Anyone could tell me any idea to solve or find a way to a solution is welcome…
Maybe few modules to load with the kernel have been removed ?

Best regards,
Pascal

As discussed on Facebook, see :
https://bugzilla.suse.com/show_bug.cgi?id=966255 (disabling plymouth works fine)
https://bugzilla.suse.com/show_bug.cgi?id=804607 (plymouth monitor output error)

Pascal