BTW, have you tried booting without intel_iommu=off? Usually such settings are meant as a stopgap. Perhaps the newer kernel and/or a UEFI update fixed it in the meantime.
FWIW, I remembered @avb66 hint:
Thought I was clever, while doing:
sudo mount -o remount,rw /var/lib/snapd/seed
sudo editor /var/lib/snapd/seed/EFI/ubuntu/grubenv
I wasn’t. 
Thought I’d save you from a boot loop.