notifications not sent with planned publication

Hello,
First of all, I know it's weekend, I'm not expecting a reply before Monday

There is an issue with the notifications for a new blog on rusland-colleges.nl
On this site the blogs are written beforehand, and publication gets planned for a later date. After publication no emails are being generated. The mail-activities list stays empty.

Resending the notification to the subscribers manually (form the list of posts in the backend) does work.
The emails appear in the list and are being send according to the cronjob.

So something goes wrong somewehere. I hope you can help!

Best regards
Ineke