[SalesForce] Developer Sandbox Refresh Status Stopped

UPDATE: Dev sandbox refresh is completed after 5 hour in stopped phase. But I'd still like to now what causes this.

Today I tried to refresh a developer sandbox in our org. First it was in queue as usual but then after some time I saw it has stopped. I've searched for the cause but did not find anything.

why would a developer sandbox refresh status change to stopped? It seems like there is nothing to do about it. No button, nothing available to change status.

And I've noticed lately even developer sandbox refreshes takes too much time. I think it became slow in Winter 16. Before Winter 16 I remember 10-30 minutes refreshes for normal org with some classes/triggers but now same orgs with no changes takes at least 4-5 hours even sometime more than 10 hours to refresh.