Hi,
I had some similar lock issue with applyEdits some times ago. It was due to too many applyEdits request sent to the AGS Server at the same time. To my part, AGS process that like if each request came from different client thus, the last request was blocked.
Could you check with Fiddler or the browser network console like Firefox if you send only one applyEdits at the same time. If not you should find a way to limit that at one at the same time.
Perhaps you could try to limit the maximum number of instance at 1 as parameter when you are publishing your feature service.
I hope it will help you.
Ben.