[proboscide99]

Hello, as suggested by kovidgoyal, after trying all hints I decided to post my debug log.
I just installed calibre 3.21 on linux mint 19 (Tara).
When I connect my kindle paperwhite via USB, the disk is automatically mounted and I can browse the files. Unmounting the device (as suggested) does not help. The kindle is not in airplane mode. I don't know the device's version, I bought it one month ago.

Here is the log:
calibre 3.21 embedded-python: False is64bit: True
Linux-4.15.0-74-generic-x86_64-with-LinuxMint-19-tara Linux ('64bit', '')
('Linux', '4.15.0-74-generic', '#84-Ubuntu SMP Thu Dec 19 08:06:28 UTC 2019')
Python 2.7.17
Linux: ('LinuxMint', '19', 'tara')
Interface language: None
USB devices on system:
[['0x46d', '0xc326', '0x7900', u'Logitech', u'USB Keyboard', u''],
['0x46d', '0xc03e', '0x2000', u'Logitech', u'USB-PS/2 Optical Mouse', u''],
['0xbda', '0x129', '0x3960', u'Generic', u'USB2.0-CRW', u'20100201396000000'],
['0x8087', '0xa2a', '0x1', u'', u'', u''],
['0x1949', '0x324', '0x401', u'', u'Internal Storage', u'G000PP12926309UX']]

No disabled plugins
Looking for devices of type: MTP_DEVICE
No MTP devices connected to system

Looking for devices of type: SMART_DEVICE_APP
All IP addresses {'lo': [{'peer': '127.0.0.1', 'netmask': '255.0.0.0', 'addr': '127.0.0.1'}], 'eno1': [{'broadcast': '192.168.0.255', 'netmask': '255.255.255.0', 'addr': '192.168.0.42'}]}
No device is connected

Looking for devices...

Devices possibly connected: None

Any suggestion?

Thanks a lot in advance and regards
Alessandro, Italy