Hi, are you using a single navmesh for a large map? Also, depending on the shape of your terrain, having a navmesh doesn’t guarantee a valid path between the AI and your player. Press P on the level editor to visualize the navmesh areas. You may need to increase Z scale to fit everything.
For large maps, there’s a blueprint class named “navigation invoker”, actor components that can be added to bots or any other actor in the level. Take a look at these videos below:
NavMesh Recast From A-Z; Optimize Your NavMesh & Fix Problem Areas; UNREAL ENGINE (youtube.com)