Just updated the Mac build with some fixes that should help with your problem! Try re-downloading the Mac build and see if it helps in any way. If it doesn't though feel free to update with any future crash logs so I can investigate further.
Getting close! Just updated the upload with some more fixes. Seems adding parallelism in some places caused more problems than benefits(and cache-abuse for that matter). I also added some progress-bar feedback that should show on the bottom right of the composition window. Lemme know how it goes and I'm so sorry for the problems you've had to face.. If it still refuses to be stable I'm also totally open to refunding you.