Let me share what I understand and know about this matter, Sales.

If you are connected with a third party to sync all transactions, it will save in the QuickBooks systems and will not disappear from our system. 

On the other hand, may I know what transactions that sync in QuickBooks using a third-party app? Any additional details will help me provide accurate data and resolutions as soon as possible. 

If you find yourself disconnecting a third-party app or transferring ownership to another user, you can see this article: Transfer app ownership or disconnect apps. 

If there’s anything else you need help with in managing your transactions, feel free to reach back out. Have a great day!