dmesg -H please, because I'm way too lazy to parse epoch ts myself

.
I'd double check your udev rules, in case something stupid is happening on USB plug and mistakenly matches on the Kindle...
EDIT: Did you also happen to upgrade your kernel? From which version to which version?
There's probably VFAT shenanigans happening on Kindle w/ recent kernels if something's doing nasty things on automount...
c.f.,
https://bugs.launchpad.net/calibre/+bug/1834641 &
https://bugzilla.kernel.org/show_bug.cgi?id=203973