I'm running a server, and when I generated the world, the server software hung on the preparing spawn area stage, and in the server log it told me that this was an issue that needed reporting, so here I am. You may notice that hbm is also partially responsible for the worldgen lag, so I'm reporting it to them as well.
latest.log

This is an issue that forge overreports in 1.12, it's not really an issue.