I just bought a Seagate 1 TB USB 3.0 external Harddrive today for around 45 bucks/euros. Now i checked this drive before on a different computer (xubuntu) it was ok. i left it at NTFS EXFAT as it came so from the stores. i booted my Batocera pc (batocera on hdd installed x86/64) and pressed F1 for the file transfer menu. i connected the USB 1 TB Seagate drive, and i just plainly copied all folder in /SHARE to this drive. after an hour or two it was done, and i ejected using the eject icon next to the drive´s name on the left panel. this happened real quick btw, and i just exited to es/batocera. i was able to quit/shutdown in an instance - which already incated something was going wrong here.
when i plugged in this new Seagate HDD to my other computer i was not able to find the drive, i saw the icon but when clicking/connecting it it gave the error 12. (xubuntu 20.04lts) so it appeared the drive was ejected to soon, therefor corrupting it. i tried the whole procedure again after having formatted the new USB HDD to ext4, and with the same result - even though i waited 10 mins after having ejected it before shutting down the batocera system (pc).
anyway, i then just copied everything by ethernet to my other computer from the batocera pc, and then copied it all to the Seagate USB HDD, which worked.
i dont know where to report this or if it needs to be reported, but it seems some media is ejected too quickly, (2-5 seconds) possibly causing this. there is no clear visible way to see if USB storage media has been ejected properly on the other hand from within the File manager (F1).