I have the very same problem. And I thought that wordfence plugin was blocking it.Finally I managed to solve this.
The problem that the cron event “nxs_querypost_event” (which is the one that activates de autoreposter) didn’t exist, so I had to create it. It’s easy to create cron events with the plugi Wp-Crontrol.
Also, my theme (ionMag) was blocking the non-default cron-scheuldes (I could only select every hour, day, week or month), so I has to change to another theme so I could scheulde the event every 15 minutes.
RU, how did you discover that nxs_querypost_event didn’t exist? And how did you find out that your theme was blocking cron schedules?
Any settings to make the existing theme work? I don’t want to change the theme, wondering what needs to be done to get this working.