@MikeLvG I CANNOT answer what may have gone wrong with your shutdown-reboot.
But I offer some ideas
DO NOT EVER save sessions on a USB stick. (Oh it will work, but ...) USB sticks are terrible!!! ... for a number of reasons. If you want to save your sessions from ANY forum distro, put in on your PC's system drive. In other words, create a partition. I recommend that if you do create a partition, you make it linux formatted (ext2/ext3/ext4) and I also recommend you create a folder on that partition named Sessions; for good housekeeping purposes. I label my partition I use for my sessions as "Persistence"
ALL of distos I use from this forum are guided to keep saves in the Sessions folder, described above
Consider if you find this pathway reasonable.