Bypass ComfyUI's torch.library.custom_op schema-registration bug that causes Flash Attention to silently fall back to SDPA (schema_.has_value() INTERNAL ASSERT FAILED).
https://github.com/love530love/ComfyUI-FixFlashAttnSchema
git clone https://github.com/love530love/ComfyUI-FixFlashAttnSchema
comfy node install fix-flash-attn-schema