Sorry it was a fast and bad answer.
There's a math that puts together: delay * samplerate / blocksize. :
   int nbufs = sys_schedadvance * as.a_srate / (blksize *1000000.);
Here "nbuf" gets a negative value (due to integer overflow) for delay 80 blocksize 64. Of course its noticeable because it sounds horrible or "no sound" iirc.
Thanks Lucas, 80msec was exactly what my colleague is using. We are testing with other values now and will get back to you. Just to get this correct, are all versions before the new "test" version that Miller mentioned affected, so also her 0.51.4? Or only 0.52.0-test1?
best, P