This has happened to two friends of mine in the past few weeks. They lost over 300 troops, a bunch of trade goods and enough decent gear for them to be considered "armed". It's not from inactivity or being kicked out of a fief. Of course they were immediately attacked and lost everything. It's a very discouraging bug. One of my friends stopped playing because of all his hard work going down the drain.
I'm pretty sure the devs won't compensate them for their losses but it would be nice if this was fixed.