The specific issue (the bad return from printf) was worked in LP #1879987 - it was fixed recently on initramfs-tools versions:
0.122ubuntu8.17 (Ubuntu 16.04 - Xenial)
0.130ubuntu3.11 (Ubuntu 18.04 - Bionic)
0.136ubuntu6.3 (Ubuntu 20.04 - Focal)
0.137ubuntu12 (Ubuntu 20.10 - Groovy)
I'll nominate this LP for initramfs-tools and set as Fix Released. If that's still reproducible in any way, likely there's another correlated issue, please open another LP and mention it here.
Cheers,
The specific issue (the bad return from printf) was worked in LP #1879987 - it was fixed recently on initramfs-tools versions:
0.122ubuntu8.17 (Ubuntu 16.04 - Xenial)
0.130ubuntu3.11 (Ubuntu 18.04 - Bionic)
0.136ubuntu6.3 (Ubuntu 20.04 - Focal)
0.137ubuntu12 (Ubuntu 20.10 - Groovy)
I'll nominate this LP for initramfs-tools and set as Fix Released. If that's still reproducible in any way, likely there's another correlated issue, please open another LP and mention it here.
Cheers,
Guilherme