“_multiDrawInstances” This property is null by default in the official documentation. I’m not sure if the multiDrawArraysInstancedWEBGL WebGL feature inherently has poor performance…
The _multiDrawInstances property is part of the BatchedMesh API, which is intended for drawing many instances of different geometries in a single draw call (by a single BatchedMesh). If you have many draw calls / Meshes — and the overhead of those draw calls is affecting performance — then replacing them with BatchedMesh might reduce the overhead and improve performance.
From your post, though, I’m not sure how you’re using it or whether a performance improvement can be expected for that use case.