I've replicated this issue in my sample QuickBooks Online (QBO) account, and it seems to have worked. Let's try performing some basic troubleshooting steps to fix the problem since sometimes cache stored up in the system can cause unexpected behavior in the product. You can start by opening a private (incognito) window. Using a safe browser and accessing the program from there can usually fix the issue.
Here's how to open it:
Once done, try to edit the invoice again. If it works, then your main browser causes this kind of issue.