Comment 12 for bug 1848856

Yes, my rpool is mirrored.
  pool: rpool
 state: ONLINE
status: Some supported features are not enabled on the pool. The pool can
 still be used, but some features are unavailable.
action: Enable all features using 'zpool upgrade'. Once this is done,
 the pool may no longer be accessible by software that does not support
 the features. See zpool-features(5) for details.
  scan: scrub repaired 0B in 0 days 05:45:25 with 0 errors on Sun Oct 13 06:09:31 2019
config:

 NAME STATE READ WRITE CKSUM
 rpool ONLINE 0 0 0
   mirror-0 ONLINE 0 0 0
     wwn-0x5000cca24ce19a84-part1 ONLINE 0 0 0
     wwn-0x5000c5004e60c802-part1 ONLINE 0 0 0
 logs
   nvme-eui.00000000010000004ce00018dd8c9084-part2 ONLINE 0 0 0
 cache
   nvme0n1p4 ONLINE 0 0 0

errors: No known data errors

In 10_linux_zfs, there is an if statement that echos data:

    if [ -n "${initrd_list}" -a -n "${kernel_list}" ]; then
        echo "${dataset}\t${is_zsys}\t${machine_id}\t${pretty_name}\t${last_used}\t${initrd_device}\t${initrd_list}\t${kernel_list}\t${last_booted_kernel}"
    else
        grub_warn "didn't find any valid initrd or kernel."
    fi

The problem is that execution time, the last 3 parameters are dropped even though they have data.

+ [ -n /ROOT/ubuntu@/boot/initrd.img-5.3.0-18-generic|/ROOT/ubuntu@/boot/initrd.img-5.0.0-32-generic|/ROOT/ubuntu@/boot/initrd.img-5.0.0-31-generic|/ROOT/ubuntu@/boot/initrd.img-5.0.0-29-generic -a -n /ROOT/ubuntu@/boot/vmlinuz-5.3.0-18-generic|/ROOT/ubuntu@/boot/vmlinuz-5.0.0-32-generic|/ROOT/ubuntu@/boot/vmlinuz-5.0.0-31-generic|/ROOT/ubuntu@/boot/vmlinuz-5.0.0-29-generic ]
+ echo rpool/ROOT/ubuntu\t-\t6d41e97f07794e0b9d409db9a99529a5\tUbuntu 19.10\t1571542278\t/dev/sdc1

You can see from the expanded debug of the run (set -xv) that both initrd_list and kernel_list had data that included the kernel and initrd but within the if, it gets dropped. That is causing the generated grub.cfg.new to be missing the kernel, initrd, and the advanced submenu items that would normally be generated.