It looks like your GRUB file (
grubx64.efi) is missing from the ESP; or perhaps Boot Repair isn't finding it for some reason (I've heard of this happening on occasion). You've also got a number of errors relating to your ESP; summarizing a few of them:
mkdir: cannot create directory '/boot/efi/EFI/ubuntu': Input/output error
[ 382.544276] FAT-fs (sda2): error, fat_get_cluster: invalid cluster chain (i_pos 0)
[ 382.544283] FAT-fs (sda2): Filesystem has been set read-only
Error: no grub*.efi generated. Please report this message to firstname.lastname@example.org
Overall, it looks like the filesystem on
/dev/sda2 is damaged. You should repair this. In Linux, the
dosfsck utility can do the job, as in
sudo dosfsck /dev/sda2. If that doesn't work, you should back up all the files, use
mkdosfs (or GParted) to create a fresh FAT32 filesystem on
/dev/sda2, and restore the files to the filesystem. You may also need to change the
UUID= value in
/etc/fstab to refer to the partition by the new "UUID" value if you re-create it.
This type of problem can be caused by the Windows "fast startup" feature, which might as well be called the "don't play nice with other OSs" feature. Basically, instead of shutting down properly, Windows uses a suspend-to-disk type of feature. This leaves its filesystems in an inconsistent state, which can then cause filesystem damage if anything but Windows is booted next. You should disable this feature to make it safe to dual-boot with Linux; however, be aware that this will result in longer Windows boot times. In fact, you might want to do this before using
dosfsck on the ESP, or run
dosfsck again after disabling the fast startup feature, just to be on the safe side.
Once you've fixed the filesystem and disabled Windows' fast startup, you'll be left with the issue of getting booting to work normally. It appears that your GRUB file has been removed. Running Boot Repair again will probably fix this; however, I'm not a fan of Boot Repair. It takes a rather heavy-handed approach that can cause further problems down the road. If you run Boot Repair, open the Advanced Options and uncheck the "Backup and Rename EFI Files" option. This will rein in Boot Repair's overzealous changes. If the result doesn't boot, though, you may have one of the rare computers that actually needs this type of hackish workaround, so you may need to run it again without disabling this feature.
Another option is to try my rEFInd boot manager. You can try booting with the CD-R or USB flash drive image. Chances are that will boot successfully even as your computer is right now (damaged ESP and all). If it works and you like rEFInd, you can install the Debian package; but do this only after disabling Windows' fast boot feature and repairing the damage to the ESP's filesystem.