Communications emails not sending

I have dev site with a number of email triggers setup. They were all tested and working fine, but now they have stopped being triggered.

I can use the send to me function to send a test to wp admin - works fine. On signup the user gets the wordpress username/password email - works fine, but the immediately on signup emails do not trigger at all.

I have tried deactivating and reactivating, I have also setup new emails, but nothing will trigger them.

Any ideas? The only thing to have changed in the dev environment from the previous successful tests is that it has moved onto a secure address for final testing as the live site will be secure too.

Thanks