Created attachment 6614 mount result I can plug a usb in and it mounts perfectly. I can unmount - that works too. If I however eject the usb - it remounts. Thunar 1.6.10-2ppa1~16.04 from https://launchpad.net/~xubuntu-dev/+archive/ubuntu/xubuntu-staging Not sure what information would be useful to provide here.
added dmesg to the attachment
Created attachment 6615 updated text
Created attachment 6616 updated text
This appears to be a kernel bug - I've recently tested patched kernels on Xubuntu Xenial and Yakkety and the issue is fixed on those. Expecting same to land for Xubuntu Zesty.
which has
Looks like this is a kernel bug.