What do I say about why I left my last job?

I have an interview next week and I am unsure how to explain why I left my last job as a production planner. Thank you in advance. I also do not want to seem like a risk. What do you say?

Say it plainly and move on to what you can do. Interviewers usually move on if you do.

Thanks for writing this out. I went through something close to it last year, and it settled down once I kept a simple log of every call and form.