Hello
I think there is a problem with new kernel.
To reproduce it try opne console with dmesg -w command, connect usb drive (fat 32) and mount it by clicking in pcmanfm.
Till now everything is ok, but after unmountig usb drive, removing from usb and subsequently plugging in, when you try to mount, there are errors in dmesg log.
From now every attempt to mount usb drive gives these errors.
You can try to copy same files to drivie but their size is alway 0 bytes after reconnecting drive.
There was no errors in kernel 4.9.