Help for anyone having this boot issue: got this while zfs-initramfs have been installed from debian backports (version 0.8.6-1~bpo10+1, due to invalid priorities) instead of pve version 2.0.4-pve1
Solved it by doing a rollback to last zfs snapshot of rpool/ROOT/pve-1 (when zfs helps fixing...
Having a unprivileged lxc container running docker container fine with 5.4.78-pve kernel
Made the kernel upgrade, docker container can't start after, here is the error :
docker run hello-world
docker: Error response from daemon: OCI runtime create failed: container_linux.go:370: starting...