@A_boas lo primero desactivar el automount (está en inglés) pero es fácil:
In ubuntu you can switch off usb automount:
"Configuring Automounting
To enable or disable automount open a terminal and type dconf-editor followed by the [Enter] key.
Browse to org.gnome.desktop.media-handling.
The automount key controls whether to automatically mount media. If set to true, then Nautilus will automatically mount media such as user-visible hard disks and removable media on start-up and media insertion.
There is another key org.gnome.desktop.media-handling.automount-open. This controls whether to automatically open a folder for automounted media."
Maybe you will need to instal dconf first (sudo apt-get install dconf..)
Lo segundo mirar si hay errores en la tabla de particiones de la emmc:
GPT tables can be fixed with gdisk
do "sudo gdisk /dev/(path to your device)"
enter command "v" - to verify disk
if there is some errors about corrupted gpt table, enter command "r" - means
recovery and something else I cant remember.
Now, in r menu, enter "?" - it will print possible commands. There is "e" command that will load partition table directy from disk. Try that, and end with "w" command that will write everything on disk.
After that, unplug device from computer and reconnect it again, and check it again with gdisk for errors.