Company ABN not appearing on emailed invoices

Over the last year randomly we get contacted by the customer to say our company ABN is not on the invoice. When I print or download this invoice the ABN is there and have checked all the invoice templates to be correct as previously advised in other conversations on here. All I can think of is that when I had a look at what the customer was downloading the invoice has two pages with the pay securely on the second page which this does not happen on when downloading myself from the register. I have looked at this to see where the glitch is and why it only happens randomly I just cannot figure it out. Any help would be appreciated as to why it is not reading this field only sometimes, thank you:)