Jason Decode Error on sync_render transform/1

[Jdyn]

Getting these Jason decode errors while using sync_render tranform. It works locally with small amounts of items, but with ~10k items there may be a chunking issue?

      sync_render(conn, params, query,
        replica: :full,
        transform: fn
          %{"headers" => %{"operation" => "delete"}} = msg ->
            msg

          msg ->
            Map.update!(msg, "value", &Map.put(&1, "path", construct_full_url(&1)))
        end
      )

2025-10-18T06:25:09.851 app[2860310b6077e8] sjc [info] 06:25:09.851 request_id=GG-B0ANU58ozmvoAASDx [error] ** (Jason.DecodeError) unexpected byte at position 0: 0x28 ("(")

2025-10-18T06:25:09.851 app[2860310b6077e8] sjc [info] (jason 1.4.4) lib/jason.ex:92: Jason.decode!/2

2025-10-18T06:25:09.851 app[2860310b6077e8] sjc [info] (phoenix_sync 0.6.0) lib/phoenix/sync/electric.ex:607: Phoenix.Sync.Electric.map_response_body/2

2025-10-18T06:25:09.851 app[2860310b6077e8] sjc [info] (phoenix_sync 0.6.0) lib/phoenix/sync/electric/client_adapter.ex:64: Phoenix.Sync.Adapter.PlugApi.Phoenix.Sync.Electric.ClientAdapter.fetch_upstream/4

2025-10-18T06:25:09.851 app[2860310b6077e8] sjc [info] (myapp 0.1.0) lib/web/controllers/sync/case_controller.ex:1: MyApp.Sync.CaseController.action/2

2025-10-18T06:25:09.851 app[2860310b6077e8] sjc [info] (myapp 0.1.0) lib/web/controllers/sync/case_controller.ex:1: MyApp.Sync.CaseController.phoenix_controller_pipeline/2

2025-10-18T06:25:09.851 app[2860310b6077e8] sjc [info] (phoenix 1.8.1) lib/phoenix/router.ex:416: Phoenix.Router.__call__/5

2025-10-18T06:25:09.851 app[2860310b6077e8] sjc [info] (myapp 0.1.0) lib/web/endpoint.ex:1: MyApp.Endpoint.plug_builder_call/2

2025-10-18T06:25:09.851 app[2860310b6077e8] sjc [info] (myapp 0.1.0) lib/web/endpoint.ex:1: MyApp.Endpoint.call/2