I see a similar behaviour on my EFI system with BTRFS root on bionic, which recently upgraded to:
grub-common/bionic-updates,now 2.02-2ubuntu8.10 amd64
GRUB_TIMEOUT is overridden to be 30 seconds. GRUB_TIMEOUT_STYLE=hidden is also overridden.
Workaround for the timeout in /etc/default/grub: GRUB_RECORDFAIL_TIMEOUT=$GRUB_TIMEOUT
I see a similar behaviour on my EFI system with BTRFS root on bionic, which recently upgraded to:
grub-common/ bionic- updates, now 2.02-2ubuntu8.10 amd64
GRUB_TIMEOUT is overridden to be 30 seconds. STYLE=hidden is also overridden.
GRUB_TIMEOUT_
Workaround for the timeout in /etc/default/grub: GRUB_RECORDFAIL _TIMEOUT= $GRUB_TIMEOUT