I am having the same issues -- I am using QBO.  It worked for over a year and then 10 days ago it just wouldn't update.  I haven't changed any passwords so not sure what happened.  Amex customer service -- very reachable -- has checked over everything on their end but said it was a QB issue.  I sat on the phone for over an hour with QB and got nothing but hold music.  I also tried chat with them and nothing for over an hour.  Hopefully this yields some better response from QB