I found that our kernel issues (at least mine, maybe others are also affected for the same reason) are not actually due to a broken kernel, but rather the result of some other hidden bug. After I disabled SELinux again ([R 4.3-RC1] SELinux problems after upgrade) and tried to boot with the latest kernels, I discovered that the issue is related to display initialization or something similar.
First, I do not see the Q-password screen with the background. Only the command line appears to enter the password. After that, the boot gets stuck at plymouth-quit-wait, but without SELinux, I can switch to other TTYs and log in. Then, using journalctl, I see that the system failed at X11 initialization.
Next, the dunst.service core dumped, and everything got stuck at the point of plymouth-quit-wait.
So, the problem is with X11 initialization… and it occurs somewhere in the early steps near GRUB and the kernel or selinux loading, but the system can boot with this kernel and work at least in console mode.