Variations Disappear

New seller here, I did my first three listings. The are shirts. I have 4 colors and 6 sizes. I added all my variations and attached the same UPC code to all of them. Saved it, everything was fine and then I go to check the listing but it looks like they deleted a portion of my variations. Tried to re-add them and then it says that this size or color conflicts with this size or color and something about asin. I added a new UPC code for just the missing sizes and colors and they still disappear. I’m beyond frustrated. If anyone knows what this is or how to fix it, please let me know.