The most possible reason why your clients view invoices differently is because of the browser they're using. Please note that the performance of QuickBooks Self-Employed depends on the browser and internet speed since this is online-based software.
There are some steps I'd like to recommend to fix this behavior. Let's start by using an incognito window and let your clients open the invoice from there. Also, you'll want to advise them to clear the cache. It's a junk file that can cause issues in QuickBooks.
Additionally, we need to make sure that they're using an updated version of the browser. I suggest Google Chrome, Mozilla Firefox, or Microsoft Edge.
I've added some links to learn more about invoicing: