my items are disappearing from nowhere, my master ball disappeared and I want her back because I was going to use the legendary please give me answer

Did you do the heatran quest? Your masterball and rare candies are taken from you by the npc there

Did you lose the Master Ball while doing the Heatran quest? If so, you can speak to Buck after defeating the lvl99 Heatran to get your Master Balls and Rare Candies back, a lvl30 Heatran will wait for you where the lvl99 one was. You can even go back to the Pokemon Center to bring your Synchronize pokemon!

If you lost it elsewhere, please let me know and i will see what i can do

make sure u havent done the pinkan island quest or the heatran quest where pokeballs n items are locked .It should not be disappearing without any reasons