@lxs Thanks for sending the reproduction project via email, we received it (we received twice the same email, with different subject title).
The issue lies with how SRP batcher sometimes behaves in a strange way, likely related to "Queue"="Transparent" and "RenderType"="Transparent" settings of the shader (and maybe also regarding the disabled ZWrite as well). It's more of a general Unity question related to how SRP batcher behaves, you can find many postings online in the Unity forums regarding SRP batcher.
If you disable SRP batcher and instead enable Dynamic Batching at the Render Pipeline Asset as follows, the draw calls are batched successfully:
A side note: GPU instancing does not affect rendering Spine skeletons at all, as the mesh is animated on the CPU (the mesh is generated and filled on the CPU).
