QNAP INTEL PMS Version 0.9.16.3
Mac OS 10.11.3 Firefox/Safari/Chrome all show the same issue.
Videos generally play fine, Direct Stream.
If I shuttle the video to rewind 30 seconds or so to rewatch something, the video will play until the point where I was and then freeze, and the spinning wheel will come up, and the video will stay there indefinitely.
If I press the X, and then resume playback from that spot it will again play fine.