Final straw with Final Cut

I have experienced numerous issues with Final Cut which are solely down to the program or the Mac I am using being glitchy. The most common is un rendered footage/ audio in the editing timeline. This is a big problem with editing because I need to be able to see which clip I am editing to make it as accurate as possible.

In the past I have been able to fix it by moving to the unloaded clip and clicking on it, then waiting for it to buffer. However I did experience a large section of Jack's vocals being missing, even after I had closed and re opened the program multiple times.

As you can see in the image the audio appears to end, however it is still there as I could hear it when I played it. Although I knew it was there, I needed to be able to see the sound waves to be able to edit accurately. Eventually I managed to get it back by zooming all the way in on the footage, then by zooming back out again. I have no idea what caused this, perhaps the size of the file had caused the program to slow down.