Comment 2 for bug 1866425

Same issue on kubuntu 20.04 updating from yesterday's daily image:

Hit:1 http://us.archive.ubuntu.com/ubuntu focal InRelease
Hit:2 http://security.ubuntu.com/ubuntu focal-security InRelease
Hit:3 http://us.archive.ubuntu.com/ubuntu focal-updates InRelease
Hit:4 http://us.archive.ubuntu.com/ubuntu focal-backports InRelease
Reading package lists... Done
Building dependency tree
Reading state information... Done
All packages are up to date.
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
1 not fully installed or removed.
After this operation, 0 B of additional disk space will be used.
Do you want to continue? [Y/n]
Setting up initramfs-tools (0.136ubuntu1) ...
update-initramfs: deferring update (trigger activated)
Processing triggers for initramfs-tools (0.136ubuntu1) ...
update-initramfs: Generating /boot/initrd.img-5.4.0-14-generic
cp: cannot create regular file '/var/tmp/mkinitramfs_6cNpmB/usr/share/plymouth/themes/spinner/watermark.png': No such file or directory
E: /usr/share/initramfs-tools/hooks/plymouth failed with return 1.
update-initramfs: failed for /boot/initrd.img-5.4.0-14-generic with 1.
dpkg: error processing package initramfs-tools (--configure):
 installed initramfs-tools package post-installation script subprocess returned error exit status 1
Errors were encountered while processing:
 initramfs-tools
E: Sub-process /usr/bin/dpkg returned an error code (1)