I looked at my /etc/initramfs-tools/initramfs.conf and noticed my COMPRESS was set to lz4. Casting my mind back that might have been attempts to solve a similar issue weeks ago. Setting it back to zstd, and following the steps in #89 sorted the problem for me.
The steps in https:/ /bugs.launchpad .net/ubuntu/ +source/ linux/+ bug/1842320/ comments/ 89 didn't _seem_ to be working for me
I looked at my /etc/initramfs- tools/initramfs .conf and noticed my COMPRESS was set to lz4. Casting my mind back that might have been attempts to solve a similar issue weeks ago. Setting it back to zstd, and following the steps in #89 sorted the problem for me.