I was having this issue, too. It used to sort automatically, then a few months ago it just stopped. New projects were added to the bottom of the list.
I realized that if you click on the little gear icon in the upper right corner of the Library tab, you can select "Keep Projects & Albums Arranged By" and check "Name"...
Mine was set to "Manual" and I have no idea why or how it changed to that (because it's always been alphabetized), but in any case, it's now fixed.