I have a ticket logged, 6987479, I received a reply saying to contact my provider as it looked like a hardware issue. My provider checked and looks like during the backup that the disk stays in readonly mode. They found these logs from when the VPS was restarted :
[ 1.123218] EXT4-fs (vda1): INFO: recovery required on readonly filesystem
[ 1.123224] EXT4-fs (vda1): write access will be enabled during recovery
[ 1.302446] Refined TSC clocksource calibration: 3292.476 MHz.
[ 1.459261] EXT4-fs (vda1): orphan cleanup on readonly fs
[ 1.893124] EXT4-fs (vda1): ext4_orphan_cleanup: deleting unreferenced inode 1068453
[ 1.912603] EXT4-fs (vda1): ext4_orphan_cleanup: deleting unreferenced inode 1049522
[ 1.952364] EXT4-fs (vda1): ext4_orphan_cleanup: deleting unreferenced inode 1831984
[ 1.952424] EXT4-fs (vda1): ext4_orphan_cleanup: deleting unreferenced inode 1831983
[ 1.954183] EXT4-fs (vda1): ext4_orphan_cleanup: deleting unreferenced inode 1831483
[ 1.954219] EXT4-fs (vda1): ext4_orphan_cleanup: deleting unreferenced inode 1831143
[ 1.996891] EXT4-fs (vda1): ext4_orphan_cleanup: deleting unreferenced inode 1831048
[ 2.008431] EXT4-fs (vda1): ext4_orphan_cleanup: deleting unreferenced inode 272384
[ 2.042169] EXT4-fs (vda1): ext4_orphan_cleanup: deleting unreferenced inode 272015
[ 2.042225] EXT4-fs (vda1): ext4_orphan_cleanup: deleting unreferenced inode 271930
[ 2.042244] EXT4-fs (vda1): 10 orphan inodes deleted
[ 2.042250] EXT4-fs (vda1): recovery complete
[ 2.114843] EXT4-fs (vda1): mounted filesystem with ordered data mode. Opts: