Problem with changing taxonomy

Since late last year, I noticed that this plugin not always changes the taxonomy of my blog posts correctly.

The cron job always fails and says it didn’t run. But, all other functions work correctly.

This is the situation. I use this plugin at an internal website for students of an art college. On this website, students can see recommended events to go and/or buy tickets for. On the homepage, I have a slider that shows all posts of a certain category. In this category, I place the not yet passed events.

Now, I use this plugin to automatically remove that category from the post when the event happens. Is it something I’m doing wrong or …?