iMovie 6.0.3 sketchy and doesn't work fully sometimes

I have a MacBook Pro, OSX 10.9.5, purchased in 2012. About half the storage is still available (250 out of 499 GB). It has 8GB of memory.

I have had iMovie 6.0.3 on here for about two years since the last OS update. It's had a problem for months where sometimes it will open the most recent file I was working on, but then I can't do anything else. Sometimes I can't start a new project.

Today, I've been starting iMovie and then trying to "Open recent" projects and it acts like it's going to open them but then they don't load.

I downloaded and installed the update for iMovie 6.0.3 and the problem is still happening.

I would prefer to avoid updating my whole OS just yet because I hear that iMovie 6 is better than iMovie 10 or 11, and I'm used to 6.

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Update:

Interesting. Rather than trying to open a previous project, I started a new project. Then I tried opening a previous project again and it worked. But I still can't edit the original project that came up when I opened iMovie.