I've checked our records and haven't seen any cases the same as yours, Becki_182-hotmai.
It looks like your clients are experiencing some browser hiccups. Let them perform some steps to fix it. To start with, let them open the invoice through an incognito window. It's the best place to identify browser issues. Here are the shortcut keys:
- Google Chrome: press Ctrl + Shift + N
- Mozilla Firefox: press Ctrl + Shift + P
- Safari: press Command + Shift + N
If they can see their invoice preview, let them go back to their regular browser, then clear the cache to refresh it.
Also, you can use a different browser to help us narrow the cause of this behavior.
If you have other questions, please don't hesitate to reach out to us. We're around to help you.