Hello,
Here the same configuration: PI3, Mate 16.04 installed on a 32GB Samsung Class10 SD Card, Samsung TV and absolutely the same problems.
I use the standard Ubuntu Mate without any additional software installed and also did no upgrade.
I found that somewhere in the audio settings a volume slider was set to zero. I set it to 100% and got some HDMI sound. But the sound is stuttering and interrupted even when I play a MP3 from the SD card with VLC.
video playback (MP4) from the SD card is only working when the VLC window is set to a very small size. When set do ~ 1/4 of full screen size, the video freezes immediately.
What to do?