I see the following error in the DMP 4K log when it tries to play an MP4. It seems like the DMP is not supporting SSL version that the server is expecting. The firmware version is 6.0.72. The same file displays fine when it is placed on a lab HTTP server, so the content is playable. I have seen identical errors while using "curl" to download files and upon upgrading "curl" the errors have gone away.
[706862.793] Playing: https://.mp4
[706862.795] TIME: PlayFile = 0.001897
[706863.289] ### 196:20:50.562 b_playback_ip_ssl: SSL connect error 1, errno 0
[706863.289]
[706863.289] 1318058000:error:14077410:SSL routines:SSL23_GET_SERVER_HELLO:sslv3 alert handshake failure:s23_clnt.c:770:
[706863.290] ### 196:20:50.562 b_playback_ip_http: B_PlaybackIp_HttpSessionOpen: ERROR: failed to setup the session, rc = -1
[706863.290]
[706863.290] ### 196:20:50.562 b_playback_ip: B_PlaybackIp_SessionOpen() ERRRO: playback_ip 0x564f8188, errorCode 10, fd -1
[706863.290]
[706863.290] Failed to setup stream: https://.mp4