Text box data missing on invoice

I have added a text box to my invoice template showing payment information for direct transfers. This has worked successfully for a few years now.  I have started receiving emails from clients that the box is blank.  Outline of text box shows but no info. The annoying thing is that it is not on every invoice. Started to see it occasionally but now about 1 in 3 invoices are emailed out with no payment details. Any ideas?