The failure does *not* occur with the ntfs and sshfs filesystems unmounted.
Since the problem is nondeterministic, I experimented for a few days with the ntfs filesystem mounted or unmounted. (The sshfs filesystem was never mounted.) With ntfs mounted, I had 11 successful suspends and 4 failures. With ntfs unmounted, I had 8 successful suspends and 0 failures.
The failure does *not* occur with the ntfs and sshfs filesystems unmounted.
Since the problem is nondeterministic, I experimented for a few days with the ntfs filesystem mounted or unmounted. (The sshfs filesystem was never mounted.) With ntfs mounted, I had 11 successful suspends and 4 failures. With ntfs unmounted, I had 8 successful suspends and 0 failures.