Thanks for bringing this to our attention with the issue you experienced when working with Sales Receipts in QuickBooks Online. Let's work together to resolve this.
Firstly, please elaborate more about the details that disappeared from the default format of your sales receipts. This way, I can lay down the appropriate information to help you fix it.
In the meantime, you'll want to check if you're using your affected sales receipt's correct default form style. You can check it from the Custom Form Style page by going to the Gear icon.
If all is accurate, excessive historical can affect the view and performance of your QuickBooks. Let's try accessing your account through an incognito window to rule out the possibility of a webpage issue. You can refer to these shortcut keys to open an incognito window in all supported browsers: