You can't really expect us to get anything out of Kindle logs from a 10 lines tail. The barest glance at those should have told you that they're *ridiculously* verbose

.
But even more interesting would be a verbose dmesg/lsusb log from a Linux *client*

.
If USBMS export is blocked (i.e., demo, I think? I don't recall the account status affecting that, and it certainly wasn't the case the last time I setup a Kindle... 4 years ago xD), it's *really* blocked: you never even see the "Connected to USB" screen.
As long as you see that one, USBMS should work (barring volumd mishaps).