problem in saving on usb HD with snap Librefoffice 6

I can not save files on usb HD, usb 2 et usb 3 linked to my machine with snap Libreoffice 6

The error message is that there is not sufficient right for this action, I do not have this problem with Libreoffice originally installed on my machine. I have Linux Mint 8.3.

Thank you for your help

(Edit: LM8 support ended April 2011; I changed tag to LM18)

it might be a snap problem?