Thanks for coming back to this thread, @MarcCH. Let me share info regarding glitches on the invoice numbers when printing invoices in QuickBooks Online (QBO).

Since you've already contacted our Support Team, you are now listed as one of our affected users and will be notified through email once updates are available. We appreciate your patience as we work to resolve this issue.

Furthermore, this article can help if you want to learn how to customize your sales forms in QBO: Personalize your sales forms.

If you ever need further assistance with printing invoices or other QuickBooks-related concerns, please don't hesitate to reach out. Have a good one.