A browser-related issue might have caused unexpected behaviors, physiotherapet-g.
There are times regular browsers store cache files that caused frequently visited sites such as QuickBooks not to function well. We can let your customers open the invoice in a private or incognito window. This type of window doesn’t any internet files. You can refer to these shortcut keys:
Press Ctrl + Shift + P for Internet Explorer or Firefox.
Press Ctrl + Shift + N for Chrome.
Hold down Command + Shift + N for Safari.
If it works, they can go back to your regular browser and clear its cache. Alternatively, they can also use other supported browsers to isolate these kinds of issues.