Invoices suddenly stop being generated

I have 2 woocommerce sites both of which worked great with the PRO version for over 3+ years.  (I do not have a log in for the support site so am unable to raise a ticket 🙁

A couple of days ago, one site suddenly stop generating PDF invoices (despatch notes are fine)  Maybe its a database issue?

I noticed, the last invoice to work left a second drop down option in the PDF drop down under order details (normally its either Dispatch note or invoice.  On this last order an additional ‘invoice’ option is present and from then on, no more working!  (see attached image) This may be nothing but just in case.