How did you record the missing transactions? What are these transactions? Are you the only user of the company file or account?
Transactions in QuickBooks Online won't be missing without a trace. Let's review the Audit Log to see the recent activities. We can see here what happened to these transactions.
I'd also appreciate if you can provide additional details (such as screenshots or steps that you took) so I can have clearer view about this. Thanks in advance!