I have the same problem with DS 212+ and my media player Xtreamer MK1 (http://www.xtreamer.net/xtreamer/overview.aspx
Before, I had a Netgear ReadyNasDuo NAS from where I played mkv files via SMB network shares : I can pause and resume the video on xtreamer so often I wanted successfully.
Now, I replaced my Netgear NAS by a new DS 212+ Nas. When I pause and resume a MKV files on xtreamer, the video starts for 2 or 3 seconds and freeze again for 10 seconds
, then starts again or stops with an error from the xtreamer, (french error message is "Support video enlevé" means "Video file missing").
So, I could pause/resume with Netgear NAS and I can't now with Synology NAS.
I don't use DLNA, just SMB share.
It seems that pausing/resuming an mkv file is like crashing the network share.
Is-there any information or correction about this problem ? Thanks