Yes we have been having this issue for some months now,  it appears to be getting worse.

Issues happening in a random way and with customers who we have had no issues with in the past.

Quickbooks support fairly unhelpful... some suggestions included 'sending customers a screenshot' or 'posting a printed copy to the customer' ! 

This issue is a worry for some obvious reasons... impact on cashflow, quickbooks users reputation with their own customers... etc etc.   However Intuits approach to this issue is even more of a worry.... is our data safe?  Could we be put in a position where our data is inaccessible or lost?  I have to say I'm really seriously worried about our reliance on this service which seems more and more fragile.