Tried downloading from emacsformacosx.com (both the nightly and the stable version), still have the same issue - I’ve also recreated the file with your echo command. Not sure why it breaks like this, since the preinstalled emacs opens the file just fine. 

What I did notice is, it seems to allocate a bunch of memory every second or so when opening that test file (looking at activity monitor -> Info about the process); before I force-killed it, it was taking up 2,39GB of ram and it didn’t seem like it would stop.

I’m attaching a sample of the process, maybe this can be of help. 

Thanks for trying to help!