CI build console high CPU usage

Chrome 49.0.2623.28 beta (64-bit) Mac OS X
Gitlab 8.4.2 8d07b81

Opening a build which is still in progress, enabling auto-scroll, I see Chrome (specifically the Google Chrome Helper that corresponds to this tab in my browser) taking up 100% of one core.

CPU profile snapshot follows:

Is there any other debug output/profiles I can provide to help track down the cause?

Thanks