In summary, /etc/initramfs-tools/conf.d/resume is obsolete.
The resume process is supposed to be driven by kernel command-line parameters resume and (optionally) resume_offset (which can be set by a script during update-grub) and the script /etc/initramfs-tools/scripts/local-premount/resume.
Please see my comments at https:/ /bugs.launchpad .net/ubuntu/ +source/ initramfs- tools/+ bug/1644975/ comments/ 12 and https:/ /bugs.launchpad .net/ubuntu/ +source/ initramfs- tools/+ bug/1644975/ comments/ 10.
In summary, /etc/initramfs- tools/conf. d/resume is obsolete.
The resume process is supposed to be driven by kernel command-line parameters resume and (optionally) resume_offset (which can be set by a script during update-grub) and the script /etc/initramfs- tools/scripts/ local-premount/ resume.