Hello and welcome to the Community, Sam
We appreciate you reaching out about your loading issue when creating invoices.
QuickBooks Online is a web-based application that uses browser cache and cookies to run faster. From time to time, these can also block web pages from loading as expected. We recommend clearing your browsers cache and Intuit-specific cookies as a first step when experiencing such issues.
You can also log into QuickBooks on a different web browser or incognito web page to troubleshoot. If this doesn't fix, please get back in touch below!