I had a friend testing this on a Mac, and he did not experience any freeze.
I'm using iMac G5 running with Mac OS Tiger, what is your friend Mac & OS ?
I'm using arduino version 15, what is your arduino version to compile then download ?
You tested again with my latest sketch, right ?
I believe so, tested the sketch you sent me by mail yesterday but to be sure, please send me again your last sketch.
BTW. Do you happen to have a java scope window providing time scale ?
Do you have any errors in "dmesg" about the ftdi driver ? I often have.
We did test together via skype chat yesterday, no error message at all.