I suspect I've met the same issue in a more reproducible way.
topology is hub (1 central "server" to which several "clients" are connected).
I create a sizeable directory on a client synced branch (a few 10s files totalling a few 100s MB).
While the directory is synced up to the server and distributed to the clients, I remove or rename the directory on the same source client.
Sync seems to get locked up with many 'Parent is not a directory' errors on the hub or clients.
I hope this helps finding the critter. This is definitely a recent issue: 0.14.18 or perhaps since 0.14.17