Hi weisztile,
Thanks for reaching out about this. Having access to your customers and records is essential in the running of your business, and I want to make sure you're able to.
The Audit log in QuickBooks Online is a great tool that keeps track of everything that's going on in the software. From user sign-ins to changes in settings, this tool presents everything you need to monitor your account. I'd strongly recommend having a look to make sure nothing was done in your account that could have led to the missing of your transactions. To do so, simply go to the Gear icon > Audit log, and feel free to review this article to learn more about the feature: Use the audit log in QuickBooks Online
If the Audit log doesn't display a change by a user leading to the missing of your data, it could be a browser issue causing this problem. Temporary internet files that accumulate in your browser can sometimes cause bugs in the software. To ensure your app or browser is running the program as designed, I recommend following the troubleshooting steps in this article: Clear cache and cookies to fix issues when using QuickBooks Online
I hope this helps you get back on track! Feel free if you have more questions.