Original setup was fine and everything worked. Then ran into some issues:

1. No Sound (was testing with snes)

First, reboot after: /boot/config.txt <- either add or uncomment the line "hdmi_drive=2"
It then worked, but after reboot stopped working, so:
$ sudo apt-get remove pulseaudio
$ sudo apt autoremove
$ sudo /etc/init.d/alsa-utils reset
$ sudo reboot

2. No Sound in specific emulators (megadrive/gameboy/nintendo, snes worked per step 1)

Delete retroarch.cfg from each emulator under /opt/retropie/configs/<emulator>/ <–it’ll regenerate

3. Backspace doesn’t work as hotkey any more

Removing the exit_emulator_btn from /opt/retropie/configs/all/retroarch.cfg

4. 2 Player doesn’t work.

Retropie menu through emulationstation, one of the sys configs. By default Player 1, 2…5 or whatever are disabled or unset. Do not do this with hotkey (backspace) + D (<- retroarch menu….changes seem to not be saved and game specific)