Hi,
I am afraid you have done all the troubleshooting steps and there does not seem to be any issue with your environment. Your issue remains a mystery to me. I am not able to replicate it on my staging website.
In this case, I am sorry but I will not be able to help because I will need to physically troubleshoot your issue in your website, but this is not possible on this forum.
By the way, I notice you have a previous support ticket ( https://www.ads-software.com/support/topic/how-to-save-invoice-template-2/ ) which you have mentioned that you have edited some source code. If you have edited anything that will affect the invoice UI, please remove your custom edit and redo again.
I am sorry, that’s all I can provide for this issue.
Have a nice weekend.
Thank you