To fix this, let's access your QuickBooks Self-Employed (QBSE) account in a private browser. There are times that the browser is full of frequently-accessed page resources, thus causing a problem when running websites, like QBSE.
Here are the shortcut keys you can use:
Google Chrome: click Ctrl+ Shift + N
Mozilla Firefox and Microsoft Edge: press Ctrl+ Shift + P
Safari: hit Command+ Shift + N
If you can successfully log in, go back to your regular browser and clear the cache. It helps to boosts the loading time of web pages and improves the performance of your system. We also advise periodically clear them to prevent web problems. If not, you can use other supported browsers.
Here's a great source that you can visit to help you record your self-employed income and expenses, track mileage, and prepare your Schedule C: QuickBooks Self-Employed Overview.
Feel free to get back here if you have other concerns about accessing your QBSE account. I'd appreciate any response and I'm always here if you need more help. Take care always.