Comment 26 for bug 1835660

Possible explanation and fix: in my case it seems the error message appeared since I enabled secure boot (which I think was disabled when I installed Ubuntu). Look below, from my journal:

Dec 05 15:07:52 elite kernel: secureboot: Secure boot could not be determined (mode 0)
Dec 05 15:07:54 elite systemd[1]: secureboot-db.service: Succeeded.
Dec 05 15:14:19 elite kernel: secureboot: Secure boot enabled
Dec 05 15:14:21 elite systemd[1]: secureboot-db.service: Succeeded.

You can see that on December 5th I booted at 15:07 without secureboot and starting with 15:14 with secureboot enabled.

And now, let's see when the error message appeared first:

$ journalctl|grep "unpacking failed"
Dec 05 15:14:19 elite kernel: Initramfs unpacking failed: Decoding failed

Now a possible fix (it was possible for me, it might be possible for you too):

What I did is that I switched compression to gzip, the message dissapeared, then back to lz4, still there is no sign of error (same result as tom in #18). My guess it that there is no need to switch it to gzip and back to lz4, but just regenerate initramfs (which we did after changing compression) with "sudo update-initramfs -u".

Maybe this takes into account that now I have secureboot enabled and generates a "compatible" initramfs.

Someone else should confirm if the fix works for them too, then I guess this bug can be closed.