To verify if anyone logs in to your QuickBooks account, I'd suggest visiting the Audit log page. From there, you'll see the list of the company's activities, the changes made, and who made them. Also, you're able to see why almost all information is missing and you only showing invoices and payments from two clients.
Click the Gear icon in the upper right corner.
Select Audit Log.
Select the Filter panel to filter User, Date, or Events and narrow the results.
If the issue persists, it might be your regular browser is experiencing some issues. That's why some details and invoices are missing. I recommend logging in to your QuickBooks account using a private browser. This is to rule out the possibility of a webpage issue, and private browsing doesn't store local files or cache.
Use these keyboard shortcuts based on the browser you're using.