What I have commented (notice of discordance of gparted in the geometry of the disk) always happens (with USB SSD, USB flash, USB hard disk, and microSD flash).
If, with gparted, I change the system partition from FAT to FAT32, as gparted suggests, then CoreELEC stops working, which seems normal to me, for this reason, I only repair the geometry in the partition but if I do not repair the geometry then CoreELEC also works.
With other firmwares ‘img’ (to install with Windows Rufus or Windows Win32DiskImager) that I try (for example enigma2) this does not happen.