Latest MM2 and Microsplat - ArgumentOutOfRange

Using a texture layer index of 3 in MM2's Microsplat Output node results in the below error, and the terrain fails to generate. Using MM2 version 2.1.10 and Microsplat version 3.9.20 in a fresh project, Unity 2021.1.27f1:

Thread failed: System.ArgumentOutOfRangeException: Specified argument was out of the range of valid values.
Parameter name: index
at System.Array.InternalArray__get_Item[T] (System.Int32 index) [0x00009] in :0
at (wrapper managed-to-managed) Den.Tools.Matrices.MatrixWorld[].System.Collections.Generic.IList`1.get_Item(int)
at MapMagic.Nodes.MatrixGenerators.TexturesOutput200.BlendLayers (System.Collections.Generic.IList`1[T] matrices, System.Collections.Generic.IList`1[T] masks, MapMagic.Terrains.Area area, System.Collections.Generic.IList`1[T] channelNumbers, MapMagic.Products.StopToken stop) [0x000eb] in F:\Exbleative2\UnityProjects2\MM2MicrosplatOnly\Assets\MapMagic\Generators\Matrix\Runtime\TexturesOut.cs:206
at MapMagic.Nodes.MatrixGenerators.MicroSplatOutput200.Finalize (MapMagic.Products.TileData data, MapMagic.Products.StopToken stop) [0x0023d] in F:\Exbleative2\UnityProjects2\MM2MicrosplatOnly\Assets\MapMagic\Compatibility\MicroSplat\MicroSplatOutput.cs:140
at MapMagic.Nodes.Graph.Finalize (MapMagic.Products.TileData data, MapMagic.Products.StopToken stop) [0x0002b] in F:\Exbleative2\UnityProjects2\MM2MicrosplatOnly\Assets\MapMagic\Nodes\Graph.cs:964
at MapMagic.Terrains.TerrainTile.Generate (MapMagic.Nodes.Graph graph, MapMagic.Terrains.TerrainTile tile, MapMagic.Terrains.TerrainTile+DetailLevel det, MapMagic.Products.StopToken stop) [0x00070] in F:\Exbleative2\UnityProjects2\MM2MicrosplatOnly\Assets\MapMagic\Terrains\TerrainTile.cs:717
at MapMagic.Terrains.TerrainTile+c__DisplayClass48_0.b__0 () [0x00000] in F:\Exbleative2\UnityProjects2\MM2MicrosplatOnly\Assets\MapMagic\Terrains\TerrainTile.cs:624
at Den.Tools.Tasks.ThreadManager.TaskThreadAction (Den.Tools.Tasks.ThreadManager+Task task) [0x00000] in F:\Exbleative2\UnityProjects2\MM2MicrosplatOnly\Assets\MapMagic\Tools\ThreadManager\ThreadManager.cs:138
UnityEngine.Debug:LogError (object)
Den.Tools.Tasks.ThreadManager:TaskThreadAction (Den.Tools.Tasks.ThreadManager/Task) (at Assets/MapMagic/Tools/ThreadManager/ThreadManager.cs:144)
System.Threading.ThreadHelper:ThreadStart