Add a note in the changelog

docs/_posts/2024-08-03-3811.md

@@ -87,6 +87,12 @@ AI - Fixed a bug with recording a platoon's plan and certain other platoon relat
 
 - (#6292) Create base state machine files for AI engineer utility machine, update state machine for tml.
 
+- (#6390) Fix a bug in the navigational mesh that could significantly slow down the simulation
+
+When we generate a navigational mesh the map is split into areas of terrain that units can walk over. This is done for each of the four layers (land, water, hover and amphibious). Heightmaps can be noisy, and therefore there can be thousands of tiny (the size of a wall) areas scattered across the map. These areas are to be culled, reducing the number of areas to take into account by a significant factor. Think in terms of going from 6000+ areas to (usually) less then 10. The culling did not work however.
+
+Some computations of the AI take into account the number of areas. These computations would blow up with thousands of areas, significantly slowing down the simulation.
+
 ## Contributors
 
 With thanks to the following people who contributed through coding: