Just chiming in.. I’m having all the same issues on 3.6.
I have an old Pi B+, and a spanky new Pi 3. I tested on both, and it seems the problem is worse on the Pi 3.
On the old Pi, I noticed the video would mostly work, but occasionally fail to play, and sometimes it would play but with no audio. I also noticed that when it failed, it was always on cold powerup. When I’d warm reboot the Pi it would always work.
On the new Pi 3, it worked once I think.. then it failed every time, cold boot or warm reboot.
So my un-technical noob theory is it has something to do with the start sequence and various things not firing up in expected, perfect order. Worse on the 3 because everything loads so much faster.
Hope the devs can fix it, because it’s pretty cool when it all works 🙂
EDIT: MORE info.. maybe related?
First.. I switched to a static picture splashscreen due to the above issue. Now when I boot the Pi 3, I see the 4 berrys, a few lines, then my splashscreen pic, then the Emulationstation loading screen. It all appears fine, but if I IMMEDIATELY navigate into a system menu and load up a rom, I see my splash pic pop up again before the rom loads. Then the controls freeze up and the screen goes BLACK with only this text in the upper left:
map: vt02 => fb0
If the rom is making sound, I hear it playing in the background, so I know MAME is still running, but I have no keyboard or control input. I was able to SSH in, but sudo reboot now did NOTHING. So I had to yank the plug.
After reboot, if I give it a couple minutes after the menu loads before launching anything, everything seems stable.