I have used their app and recommended the same in our videos too. many of our audiences have used and so far no chats history issues happened as per my understanding bro. this could be a specific issue happening with your device.
You may write to wondershare support once and see if they could help bro. normally they will ask for full chat backup. if there is no privacy issue we can share it with them.
just to redo the steps from the start and see how the issue can be recreated.