Commit Calendar Not Working

The new commit calendar is not displaying all commits, and sometimes it doesn't work at all.

In this screenshot, you can see that the user commited recently, but the commits are not shown in the calendar (the calendar shows last activity on Feb 17, more than two weeks ago).

Refreshing the page causes the calendar to stop showing any commits at all:

This sometimes happen on the first time the user profile is loaded, sometimes after reloading. For some users I wasn't able to get the calendar working at all.