Thank you for your response. Since you confirmed that there shouldn't be anything wrong with the u-boot package I did some testing and came to the conclusion that something must have gone wrong with my installation.
Backed up all the files on the partition with rsync
Flashed a fresh image of armbian and started it so it would resize
Shut down and deleted all the files on the partition of the fresh install
Copied the old files back on the new partition with rsync (and replaced the UUID in fstab)
After this I the boot was normal, and I even tried to reinstall the u-boot package just to make sure and it still works.