@heldegar
The Raspberry Pi Zero only has 512 MB as RAM, the Pi 3 for example has 1 GB RAM.

So on the Pi Zero I would suggest:
• Do not use a video output in 1080p. Forcing the 720p in the recalbox-user-config.txt is the best way to keep overall resolution "low"
• Disable the Webmanager (it takes too much ram for now)
• Keep the original recalbox theme
• Keep the number of active system low
• Do not use fullsets

@sch0s well, we will need mich more details to try to help you out. What specific issues are you having? And just to be sure... which one is the default core?

Don’t forget we don’t develop the emulator ourselves, so besides someone being able to confirm or deny the same issue happens on his/her installation, the libretro github issue tracker is the right place for you.

@deepunder Use MK Rev.3