Nurtures send, then stop

Anyone else had issues with nurture campaign's starting ok and then suddenly stopping? I had a series of 4 emails in a stream with a cadence set to send twice a week. After 1st email sent, no others in stream went out. I thought it was maybe because after I started the campaign I had to amend cadence days so as not to clash with other campaigns going out. After waiting over week to make sure Marketo wasn't just being slow to report activity, I decided there must be a fault, so I sent up a new stream with same members, put the remaining emails in to it, and activated it. Again, first email has sent (April 19th), but email 2 should have sent on Tues April 24 (but doesn't appear to have), and Email 3 should be sending today. Anybody else run in to this problem? Nurture sends first email then ignores rest of active emails? Smart list = 'Member of this nurture campaign'. Flow=Change Engagement Program stream to Try2