Issues with Gen 1 games

[Qlimax95]

Hello fellow Pokemon lovers! I was wondering if anyone could help me. ;s I downloaded Pokemon Yellow and used Pkhex so I could use them in Stadium. But every now and then when I open up Pokemon Stadium and want to use the mons that I have created in Pkhex, they end up being gone for some reason  And this doesn't happen at all in Pokemon Crystal for example. Am I doing something wrong? I truly hope someone can help me figure out why this is happening. 

[theSLAYER]

We legally can’t assist you as you pirated the games. Please understand. Have a good one.