It seems only core content types, but not newly added content types are showing up in the "Create content" section. See screenshot illustrating the problem.
I'm getting similar behaviour except it usually only picks one or two content-types randomly to display. I've cleared caches numerous times. In the mean time you can just create your own menu and add it to admin.
I'm having the same problem. I've tried rebuilding the menu structure and clearing all caches, uninstalling and reinstalling etc.
I'm going with the workaround suggested by pribeh above for now.
Having the same problem. . . it only shows the last content type I created.
Disregard my comment. I found the source of the problem elsewhere.
Drupal is a registered trademark of Dries Buytaert.