Running the test main/snapctl-configure-core on pi 2 and 3 there is a failure running this piece of code:
echo "Check that pi config handline works"
if [ -e /boot/uboot/config.txt ]; then
cp /boot/uboot/config.txt config.txt.save
snap set core pi-config.hdmi-mode=1
cat /boot/uboot/config.txt | MATCH ^hdmi_mode=1
snap set core pi-config.hdmi-mode=""
cat /boot/uboot/config.txt | MATCH ^#hdmi_mode=1
echo "Ensure the config.txt are fully undo when an option is unset"
if ! diff -u /boot/uboot/config.txt config.txt.save; then
echo "error: unexpected diff in /boot/uboot/config.txt"
Basically, what it is happening, is that the file /boot/uboot/config.txt does not contains a new line at the end of the file as it had initially, and it makes the diff to fail.
The error obtained https://paste.ubuntu.com/25728285/
It works properly on vms running ubuntu core, but it fails on boards.