Thanks for bringing this to my attention. I'm here to help determine why your transactions suddenly got deleted.
Just to clarify, since you mentioned that they weren't recorded yet, were you referring to downloaded bank transactions? If so, it would be a good idea to go to the Excluded tab and check if your transactions were excluded. Here's how:
Click Banking in the left panel.
Make sure the right bank account is highlighted. If not, then select the correct one.
Go to the Excluded tab.
Mark all of the transactions that you need to record, then from the Batch actions drop-down menu, choose Undo.
However, if you still can't find them there, then the most likely reason why your transactions got deleted is that the connected bank account got disconnected. That said, you'll need to re-connect the bank to QuickBooks again.
Please let me know how it goes on your end. I want to make sure this is taken care of. Thanks again for reaching out, I'll be standing by for your response.