I've checked our records and haven't seen any cases the same as yours, Dasecurityaz. I'll help you resolve it.
The unexpected behavior can be caused by too much cache. Let's start with signing into your account through a private browser. It's the best place to know if it's a web issue. These are the shortcut keys:
Google Chrome: press Ctrl + Shift + N
Mozilla Firefox: press Ctrl + Shift + P
Safari: press Command + Shift + N
If you're able to email the invoice, go back to your regular browser, then clear its cache to refresh the program. We advise our users to delete them now and then to prevent and fix issues like this.
Additionally, you can use a different browser to narrow down the issue.
I also started having this issue the first of the year. I switched to a hotmail account for the ability to email invoices, but that was a quick fix. I have tried everything that has been recommended online and no help. Recently upgraded QB to 2021 and still having the same issue. I don't really understand how the "cache fix" works but I will try the recommendation and see if this helps
I was on the phone with support for 4 hours today only to have them tell me that it is a yahoo problem.. He stated that quickbooks and yahoo won't work together so I tried my Gmail and it went right thtough