I submitted my first express entry profile on May 3, 2017, my CRS was 391 and had my UCI generated.
I took up IELTS exam again in June, and got IELTS scores (CLB 9) on July 8th 2017 and my CRS improved. So I withdrew the May 3rd profile and resubmitted a new express entry profile on July 16, 2017.
But for the new express entry profile, UCI is not generated yet. It's more than two weeks since i submitted my profile.
don't worry it's just normal. one's first officer verifies your file and if officer satisfied with your documents then your UCI number showing on your account in most cases. if not before medical passed UCI number will be displayed on your account.