I added games to roms. but when i tried to see it on the device, it dissapeared out of nowhere and i dont know how solve this.
Edit: Added dc and psp games and it shows. Now i dont really know how to solve this.
Without replication steps the only thing I can suggest is that you ensure that content has been safely written by safely ejecting your card from whichever OS you are running.
Almost certain this is caused by the user turning on the hide history games from romlist.
If you disabled this option your games will most likely come back, as muOS does not delete any content.