This plugin does not contain any movement components or behaviour trees. It only implements 3D pathfinding algorithms.

The CrowdSystem is currently not supported for flying agents (as it requires specific features of the navmesh).

Runtime Generation is partially supported. Setting Runtime Generation to Dynamic allows for procedural levels, or a manually triggered rebuild. However, constantly moving objects (such as moving platforms) as blocking meshes are not supported, nor are blocking rigid bodies. Please see here for more details.

Does not currently support navigation areas or modifier volumes. All areas within the octree have the same cost of traversal, however the pathfinding algorithm has various optimisations to bias the result towards larger areas. Please see here for more details.

Does not currently support level streaming, and will load the entirety of the world’s navigation data on level load. Due to the compact nature of the data structure, chunking of the octree data structure is not currently implemented. However, enabling the Spawn Nav Data in Nav Bounds Level setting in Project Settings means different navigation data can be serialised to different sublevels and manually loaded as required.

3D pathfinding is inherently not as fast as the default 2D navmesh pathfinding (due to the very large search space), and therefore finding the absolute shortest path is often not performant.
Optimisations to increase speed at the cost of accuracy have been implemented, please see here for more details.
There is also the option of asynchronous pathfinding using the C++ function:

uint32 FindPathAsync(UNavigationSystemV1* NavSys, const FNavAgentProperties& AgentProperties, FPathFindingQuery Query, const FNavPathQueryDelegate& ResultDelegate, EPathFindingMode::Type Mode = EPathFindingMode::Regular);

in UFlyingNavFunctionLibrary. From Blueprints you can use the Find Path To Actor/Location Asynchronously nodes.

Please Note: when using flying navigation, do not use the default UNavigationSystemV1::FindPathAsync, as it can cause a crash on PIE exit.

At the present time, the behaviour tree task MoveTo performs pathfinding synchronously, so optimisations are recommended for complex scenes if you are using behaviour trees.

The octree drawing code is designed to be very performant in the viewport. The octree nodes do not use the DebugDraw functions and will therefore scale very well.

However, the neighbour connection drawing does use DebugDraw functions, and should not be used for high resolution octrees.
Also, the visualisation gathering step (copying data from the navigation data to the rendering thread) will block the main thread, and runs whenever a navigation data option is modified. This means that changing options will lag slightly, depending on the currently built resolution. It's recommended to build on a lower resolution to change options, or clearing and rebuilding the navigation data.

Can only generate one octree per world per agent. Can be optimised by only placing navigation volumes around where your meshes are, as only the meshes in volumes will be taken into account. However, you can generate octrees in different places by defining multiple agent types in project settings. By creaing differently named blank subclasses of AFlyingNavigationData in C++ (one per agent type), the requirement for different agent radii and heights can be mitigated.

There are quite a few things that could lead to an AI actor being non-responsive. Listed are the most common reasons, if these don't work please open an issue on GitHub.

1. A FlyingNavigationData actor is required, which should be automatically spawned in the level (see below).
2. If an invalid default agent is selected in Project Settings, pathfinding can fail.
   
3. If using multiple agent types, make sure that at least one of the radius, height and step height of each agent is different from each other. These properties are used as a key hash in a lookup table, so if they're all the same only one is ever registered (the one furthest down the table). This logic is in UNavigationSystemV1::GetNavDataForProps, and is the source of many headaches when working with multiple agents. It's worth becoming familiar with this function if you're having issues with multiple agents.
4. The AI controller needs to be requested to move. Using MoveTo or a behaviour tree does this for you, but for the FindPath* nodes you need to use the Request Move node.
5. The PathFollowingComponent of the AIController might be a CrowdFollowingComponent. Make sure you're not using a DetourAICrowdController.
   The CrowdSystem is currently not supported for flying agents (as it requires specific features of the navmesh).

In order for pathfinding queries to work, a FlyingNavigationData actor needs to spawn in the world.
This will occur if you have done the following:

1. Created an agent in Project Settings with Preferred Nav Data set to Flying Navigation Data.
2. Checked your agent is supported under Supported Agents Mask, in both Project Settings and World Settings (under World/Navigation System Config/Supported Agents Mask)
   
3. Placed a Nav Mesh Bounds Volume in the world.
4. Reopened the level.

There are 3 options which affect a mesh's blocking status. In order for a mesh to be blocking, it must have these options:

1. Collision/Can Ever Affect Navigation = true
2. Physics/Simulate Physics = false
3. Navigation/Is Dynamic Obstacle = false in the Static Mesh asset settings.
   

Conversely, toggling any of these settings will make the mesh non-blocking.
In most cases the best option is setting Collision/Can Ever Affect Navigation = false on the Static Mesh spawned or placed in a level. The Is Dynamic Obstacle option impacts all instances of that Static Mesh, and so could be useful for always non-blocking meshes. And obviously Simulate Physics = true is a simulated rigid body.
A reload may be required before building the navigation for the changes to take effect.

This means you have pushed the Max Detail Size too far, and the node index parameter has overflowed. To fit nodes compactly, unique identifiers need to fit into a 32 bit integer, 22 bits of which are reserved for the node index in a given layer. The number of nodes in a layer has exceeded 2^22 = 4,194,304, and you should really increase that Max Detail Size. We can pretty much guarantee that you don't need it that low, but if you think you do open an issue on GitHub and we'll see what we can do.

unresolved external symbol "__declspec(dllimport) public: bool __cdecl FSVOLink::IsValid(void)const " (__imp_?IsValid@FSVOLink@@QEBA_NXZ) referenced in function "public: enum ENavigationQueryResult::Type __cdecl FSVOPathfindingGraph::FindPath(struct FVector const &,struct FVector const &,struct FSVOQuerySettings const &,class TArray<struct FNavPathPoint,class TSizedDefaultAllocator<32> > &,bool &)" (?FindPath@FSVOPathfindingGraph@@QEAA?AW4Type@ENavigationQueryResult@@AEBUFVector@@0AEBUFSVOQuerySettings@@AEAV?$TArray@UFNavPathPoint@@V?$TSizedDefaultAllocator@$0CA@@@@@AEA_N@Z)

If you wish to access the plugin C++ API, you will need to link against FlyingNavSystem. You will also need to link against the NavigationSystem module if you call parts of the built in Navigation System.
In your project .Build.cs file, you should have:

PublicDependencyModuleNames.AddRange(new string[] { "Core", "CoreUObject", "Engine", "InputCore", "NavigationSystem", "FlyingNavSystem"});

For example, in the benchmark project I use FNavigationQueryFilter to perform a path query, which requires linking to NavigationSystem.

When using a Pawn as a pathfinding goal, it is a good idea to set the Base Eye Height to zero. Otherwise, the pathfinding algorithm will use the bottom (or ‘feet’) of the Pawn as the goal location, rather than the centre. The feet are more likely to be inside a blocked area.
Note: This does not apply to Characters, which unfortunately uses a hardcoded CapsuleComponent->Bounds.BoxExtent.Z offset for the feet.

Using a sphere primitive as the simple collision on a mesh can sometimes be inaccurate, as the builtin geometry gathering code converts it to a low-res triangle approximation. This can mean bits of spheres poke out of the voxels, but this can be rectified with the Use Agent Radius checkbox under the advanced Generation options.

FNavigationSystem::GetNavDataForActor(AActor) and UCharacterMovementComponent::GetNavData() will not return a AFlyingNavigationData in 4.24, as it casts to ARecastNavMesh.
Note: Fixed in 4.25 and up.

If "Data Gathering Mode" is set to "Lazy" and "Generate Navigation Only Around Navigation Invokers" is turned on, the landscape geometry is not available on every thread. Therefore, only some octants have access to that data. The current workaround is to set Data Gathering Mode to "Instant" and reload the level. This only needs to be done at build time, so it can be changed back to "Lazy" for production.