You may eventually send or receive a single transaction, but later notice that it appears twice in your history, with the same exact value, but a few minutes apart. You will also notice that they have different IDs and only one of them affects your balance.
This is normal for cross-chain transactions and accurately represents how Kadena was designed by its creators. A future update will combine cross-chain transaction pairs into a single entry to better represent the balance change and number of operations made. You can read more about cross-chain transactions here.
If the transactions have the same ID, this is simply a synchronization and refresh problem, and not a security risk in any way. You can try swiping down on the transaction history to force a refresh, or restarting the app to clear the duplicate. If the issue persists, please open a support ticket so we can analyze possible errors on our backend database.