Keeps crashing and glitching

iMovie is a good app to make movies. But, I keep having problems with iMovie. For example Im editing a video then all of a sudden all of the voiceovers gets shifted to another scene or clip. Also sometimes in some clips there is an extra second with a plain black screen that I did not put in the vide originally. These crashes and glitches are so annoying! Get them fixed!!!!

TaylordATX about iMovie, v2.2.3