函数调用无法返回json格式参数

之前测试qwen-plus 的函数调用能力时,发现当输入的上下文较长时（total_tokens>50k）,tool_calls偶尔会出现arguments不是一个正确的json字符串，一直以为是长上下文导致的。但是现在发现输入tokens很低的情况下也会出现这种情况，谁能解答下？
结尾少一个 }号

"{\"arg0\": {\"purpose\": \"获取需求迭代记录信息\", \"type\": \"demand\", \"user_id\": \"ContextAgent\"}"

完整报文：

OpenAI Response Details:
Status: 200
Headers: vary: Origin,Access-Control-Request-Method,Access-Control-Request-Headers, Accept-Encoding
x-request-id: 4416fec4-91bc-9dc3-9542-3db4d01a349c
x-dashscope-call-gateway: true
content-type: application/json
req-cost-time: 1450
req-arrive-time: 1747261124863
resp-start-time: 1747261126313
x-envoy-upstream-service-time: 1448
set-cookie: ██
date: Wed, 14 May 2025 22:18:46 GMT
server: istio-envoy

Body:
{
  "choices" : [ {
    "message" : {
      "content" : "",
      "role" : "assistant",
      "tool_calls" : [ {
        "function" : {
          "name" : "RequirementIteration_get",
          "arguments" : "{\"arg0\": {\"purpose\": \"获取需求迭代记录信息\", \"type\": \"demand\", \"user_id\": \"ContextAgent\"}"
        },
        "index" : 0,
        "id" : "call_f4d867e83fef4159bd3fad",
        "type" : "function"
      } ]
    },
    "finish_reason" : "tool_calls",
    "index" : 0,
    "logprobs" : null
  } ],
  "object" : "chat.completion",
  "usage" : {
    "prompt_tokens" : 2336,
    "completion_tokens" : 42,
    "total_tokens" : 2378
  },
  "created" : 1747261126,
  "system_fingerprint" : null,
  "model" : "qwen-plus-latest",
  "id" : "chatcmpl-4416fec4-91bc-9dc3-9542-3db4d01a349c"
}