As I was playing on my survival world, I confusingly lost my items without knowing the real reason behind it. And I tried to redo a trade just because I had a clue that I always lost an item after I have done a trade.

And so the reason behind my items are disappearing is for example here I had a bow on the first slot and I had 4 stacks of carrots and bring some items from the 1st stack of carrots and some more from the 2nd or any from the other 3 stacks of carrots(these carrots represents the item that will replace your item), Then tap on the emerald or simply do a trade then exit then trading tab. Then surprisingly had carrots replacing my bow which the bow is on the 1st Slot on My Inventory

Steps to reproduce:
1.Get at least two stacks of items that will villagers want to buy/trade (for example a carrot, villagers want to buy/trade a carrot for an emerald)
2.Get a villager (for Example a Farmer)
3.Get an Item which will be the item to disappear for example a bow, and put it on your 1st slot of your inventory
4.And then place carrots from the 1st stack to the villager's slot where you will place your item to trade (place the whole stack)
5.Trade, or Tap the emerald (do not draw back the leftover carrots)
6.And then once you've done the first trade, Fill the leftover carrots with the other stack of carrots (which is the 2nd stack) to the villager's slot
7.And so after you done this simply do a trade and the leftovers from the trade will go to your 1st slot replacing the bow or the item that is on your 1st Inventory slot