You are referring to ICAO Annex 14 Volume I, Aerodrome Design and Operations. Section 3.9.9 says:
Recommendation.— Where slope changes on a taxiway cannot be avoided, the transition from one slope to another
slope should be accomplished by a curved surface with a rate of change not exceeding:
1 per cent per 30 m (minimum radius of curvature ...
The important word is "change" - that is, how much the slope is allowed to change - so no sudden sharp edges are allowed, but all connecting slopes (or flats) need to be rounded off by 3000 or 2500m. How much the allowed slope is - will be discussed elsewhere.