I am working in production on a course where I have one student and about 30 gradebook items. I've enabled the new gradebook and I get a delay between when I click on Grades. If I refresh, the gradebook instantly displays. This doesn't happen every time I access this course, but I also can't determine a specific cause or series of steps that will result in this.
I created this course via content important (not via csv as was noted by others as having a lag upon import). I've tested this across multiple networks and in Chrome and Firefox.