We’ve released a patch to the HH theme that fixes a memory leak (#906). 
This leak occurred when the grunt watch task was used. Builds kicked off by the watch task would retain a significant chunk of their allocated memory, even after completion. This caused an issue in live preview; previews would stop working and the console would show “Killed”.
This issue impacts Theme v1.20+. Upgrade your theme to avoid the aforementioned issue with live preview.