What is /usr/share/initramfs-tools/plymouth-hook.diverted? This looks like a local diversion on your system, not anything to do with the plymouth package; and there are no changes introduced in the SRU that would cause this problem. Looks to me like a self-inflicted problem on your system.
What is /usr/share/ initramfs- tools/plymouth- hook.diverted? This looks like a local diversion on your system, not anything to do with the plymouth package; and there are no changes introduced in the SRU that would cause this problem. Looks to me like a self-inflicted problem on your system.