Mistakes after rendering / exporting movie

Hey,

I have been working on a project in iMovie 10.1.1. After finishing the project I rendered / exported it as file and saved it on my desktop. Unfortunately, there are some mistakes in there, concerning the written text (bold / unbold) in the rendered mp4 which don't exist in the project in iMovie. I have rendered it many times, but there have always been mistakes, even though the mistakes changed to other words, not written in bold even though they should be. As I read some contirubutions to other problems from 2011, I also switched off the Time Maschine, which apperently helped some other user when they had a problem with exporting their movies, but this didn't help me neither. I also changed the quality of the video, name and rendering quiltiy but this didn't solve my problem as well.
I would be really glad if some of you had an idea for solving that problem. Thanks for your help and best regards
David