Error messages like the one you mentioned above can occur when the browser has collected too much data. Cache and cookies collect in your web browser when you visit several web pages. This is why you're able to access web pages easily because Google Chrome, Safari, etc. remember the pages you visit and stores the information in its memory. I've listed articles below that go over the steps on how to cache and cookies in different web browsers:
You can also open a private web browser that won't track data and open QuickBooks there. After opening a private window or clearing your cache and cookies, try running the profit and loss by customer report again. Now you should be able to view the report you need.
Please let me know if this gets you back to business. I'll keep an eye out for your response.