sshfs device is busy

I think you want a lazy unmount:

sudo umount -l example

Some program is using a file in the filesystem you're trying to unmount. It could be a file opened for reading or writing, a current directory, or a few more obscure cases. It could even be due to a directory on the filesystem being a mount point.

To investigate, run lsof +f -- example. It will tell what the process(es) are using the filesystem. Make your own judgement as to whether to make them close files, kill them, or defer the unmount operation.

I just had this problem and could not kill -9 the process reading from the mounted filesystem. kill -9 did not work even after fusermount -zu /mount/point or umount -l /mount/point (which worked). The only thing that worked was pkill -9 sshfs.