Since we don't have any reported issue regarding this behavior at this time, I'd suggest using a private browser to check if this is browser-related.
Please refer to these keyboard shortcuts based on the browser you're using:
Press Ctrl + Shift + N keys on your keyboard (Google Chrome)
Press Ctrl + Shift + P keys on your keyboard (Firefox or Internet Explorer)
Press Control + Option + P keys on your keyboard (Safari)
Log in to your QuickBooks account again using the private browser. Try saving or sending your invoice to check if it works. If it does, I'd recommend clearing your cache to refresh your browser and clear the stored data that may have caused some odd errors.
If the issue persists, please reach out to our Online Support so that they can further check this issue using their tools.