"Some people reporting it happens after unlocking the "combo meals", others saying it happens after reaching the next town. There is currently nothing we can do about it."
"[Critical / Game-breaking] Sometimes, after the first Rank Up conditions are announced to the player, the "Rank Up" option doesn't appear in the "Manage" menu. This blocks all research, development and progress for the remainder of the game. (Seen on Android version 1.3.0) & IOS 16.6.1" - from Kairosoft wiki
There are bugs in the game, and Kairosoft probably hasn't fixed it yet.