Rush is crashing and failing to download MP4 file onto my computer

This app has been great to use but it isn't performing as well as I think it should. I have a decenlty capable computer with pretty good specs and I can't download my finished MP4 file. Yesterday I had to try 3 differnent times as the first 2 times the download failed and crashed my computer. 

Today I had to make some edits to my video and I have already tried to download my updated mp4 file with no success.